PBN TRAININGFOR OPERATIONAL ATS … Training Study Guide.pdf · This manual is the first step...

PBN TRAINING FOR OPERATIONAL ATS

PERSONNEL

SA PBN Implementation Project

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REVISION INDEX

Version Revision Date Reason for Change Pages

Affected

Draft 0.1 03/05/2010 New Document by Zach Froneman All

Draft 0.2 04/05/2010 Amended by Zach Froneman All



Draft 0.4.1 17/05/2010 Amended by Elsabé Wait &

Zach Froneman

All

Draft 0.4.2 21/05/2010 Amended by Zach Froneman All



Zach Froneman

All


Zach Froneman

All

Draft 0.5 25/05/2010 Amended by Elsabé Wait &

Zach Froneman

All


Draft 0.5.2 02/06/2010 Amended by Elsabé Wait,

Pamela Johnson & Zach Froneman

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Draft 0.6 06/06/2010 Amended by Elsabé Wait,


All

Draft 0.6.2 14/06/2010 Amended by Elsabé Wait,


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Draft 0.6.3 21/06/2010 Amended by Zach Froneman Sec. 4

Draft 0.6.4 28/06/2010 Amended by Zach Froneman Sec. 4 & 5


Draft 0.6.6 07/07/2010 Amended by Howard Hawk, Wayne

Lessard & Zach Froneman

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Draft 0.6.6 14/07/2010 Amended by Zach Froneman,

formatting changes

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EXECUTIVE SUMMARY

The primary aim of this manual is to provide the operational ATS personnel with the required

theoretical knowledge to progress to the practical placation and use of PBN based RNAV procedures

in the daily provision of Air Traffic Services.

We will discuss the development from basic conventional navigation through to the possible

application of Performance-Based Navigation (PBN) as proposed by the International Civil Aviation

Organisation (ICAO). It also aims at providing the required reference material for the reader to

familiarise him or herself with the development, application and implications of widespread Area

Navigation (RNAV) application in a modern Air Traffic Management (ATM) System.

Recognising the current level of understanding of RNAV application, this manual will explain the flight

deck RNAV capabilities as well as the means to guarantee the navigation performance. This manual

will also explore the possible changes to the way in which ATM is provided at the moment as well as

to explain the expected benefits to the wider ATM community of increased use of the full RNAV

capabilities now available.

This manual is the first step towards the PBN training prescribed for operational Air Traffic Service

(ATS) by The ICAO. The second step will include simulation exercises that will demonstrate in a

practical manner the benefits of maximising RNAV applications.

The Body of the Document starts on Page 25

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REFERENCES

ICAO Manuals:

Doc 9613 Performance-Based Navigation Concept and Implementation Manual

Doc 9905 RNP AR Approach Design (Draft)

Doc 9849 GNSS Manual

Doc 9689 Manual on Airspace Methodology and Sep Minima

Doc 9573 Manual of Area Navigation (RNAV) Operation

Doc 9854 1ed ATM Operational Concept

Doc 9750 Global Air Navigation Plan

South African National Airspace Master Plan

ATNS ATM Roadmap.

SA PBN Implementation Roadmap

An Introduction to GNSS, Charles Jeffrey, P. Eng., NovAtel Inc, 2010.

Internet sites:

www.insidegnss.com – Engineering solutions from the GNSS community

www.spaceandtech.com – Andrews Space and Technology (AST)

www.en.wikipedia.org – Wikipedia, The Free Encyclopedia

www.igscb.jpl.nasa.gov – The International GNSS Service (IGS)

www.unoosa.org – United Nations Office for Outer Space Affairs, International Committee

on Global Navigation Satellite Systems

www.gps.gov – Global Positioning System, Serving the World

www.pnt.gov – Spaced-based Positioning Navigation & Timing

www.8051projects.info – 8051 Forum (Micro-controller projects)

www.faa.gov/air_ traffic

www.boeing.com/ commercial/aeromagazine/

www.directory.eoportal.org – Sharing Earth Observation Resources

www.gnssapplications.org – GNSS Applications and Methods

www.faa.gov – Federal Aviation Administration; GNSS Library

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TABLE OF CONTENT

REVISION INDEX ................................................................................................................................... 2

EXECUTIVE SUMMARY ........................................................................................................................ 3

REFERENCES ........................................................................................................................................ 4

TABLE OF CONTENT ............................................................................................................................ 5

ABBREVIATIONS .................................................................................................................................. 8

EXPLANATION OF TERMS ................................................................................................................. 12

1 AREA NAVIGATION (RNAV) SYSTEMS. ............................................................................... 25

1.1 Background .............................................................................................................................. 25

1.1.1 Conventional Navigation Methods and Procedures ................................................................. 26

1.1.2 RNAV Navigation Methods and Procedures ............................................................................ 29

1.1.3 WGS - 84 Geodetic Reference Datum ..................................................................................... 29

1.1.4 Historical Overview – Future Air Navigation System (FANS) .................................................. 30

1.2 Aircraft Area Navigation (RNAV) Computer System – Function .............................................. 32

1.2.1 Navigation ................................................................................................................................ 34

1.2.2 Navigation Database ................................................................................................................ 35

1.2.3 Flight Planning .......................................................................................................................... 37

1.2.4 Guidance and Control .............................................................................................................. 37

1.2.5 Display and System Control ..................................................................................................... 38

1.2.6 Manual Radio Position Updating .............................................................................................. 38

1.2.7 Automatic Radio Position Updating .......................................................................................... 38

1.3 Area Navigation (RNAV) Operations ........................................................................................ 39

1.3.1 RNAV Routes ........................................................................................................................... 39

1.3.2 RNAV Waypoint types .............................................................................................................. 40

1.4 Required Navigation Performance (RNP) – Specification ....................................................... 41

1.4.1 Functional Capabilities and Limitations .................................................................................... 41

1.4.2 RNAV System Requirements in terms of Accuracy, Integrity and continuity ........................... 43

1.5 RNAV and RNP Specific Functions ......................................................................................... 47

1.5.1 RNAV Leg types ....................................................................................................................... 47

1.5.2 Fixed Radius Paths .................................................................................................................. 49

1.5.3 Holding Pattern ......................................................................................................................... 51

1.5.4 Offset Flight Path ...................................................................................................................... 51

2 GLOBAL NAVIGATION SATELLITE SYSTEMS (GNSS) ...................................................... 52

2.1 Description of the GNSS Concept ............................................................................................ 52

2.1.1 Almanac.................................................................................................................................... 59

2.1.2 GNSS Segments ...................................................................................................................... 61

2.2 System Accuracy, Integrity, Continuity and Availability ........................................................... 64

2.2.1 Signal Performance Requirement ............................................................................................ 64

2.3 Augmentation ........................................................................................................................... 67

2.3.1 Ground-Based Augmentation System (GBAS) ........................................................................ 68

2.3.2 Aircraft-Based Augmentation System (ABAS) ......................................................................... 69

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2.3.3 Space-Based Augmentation System (SBAS) .......................................................................... 70

2.3.4 Ground-Based Regional Augmentation (GRAS) ...................................................................... 75

2.3.5 Techniques to improve GNSS receiver performance .............................................................. 75

2.3.6 GNSS Liability .......................................................................................................................... 79

2.4 Description of Receiver ............................................................................................................ 81

2.4.1 Display ...................................................................................................................................... 82

2.4.2 Functionality ............................................................................................................................. 85

2.4.3 Integrity Alerts .......................................................................................................................... 88

2.5 NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System)............ 90

2.6 GLONASS (Global Navigation Satellite System) ..................................................................... 93

2.7 GALILEO (The name given to the European Global Navigation Satellite System) ................. 95

2.8 Other Navigation Satellite Systems .......................................................................................... 97

2.8.1 China ........................................................................................................................................ 97

2.8.2 India .......................................................................................................................................... 99

2.8.3 Japan ...................................................................................................................................... 100

2.8.4 France .................................................................................................................................... 101

3 ALL WEATHER OPERATION ............................................................................................... 103

3.1 Conventional NAVAID Based Procedures ............................................................................. 104

3.1.1 Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) .... 104

3.1.2 The Non-Precision Approach (NPA) ...................................................................................... 105

3.1.3 The Precision Approach (PA) ................................................................................................. 106

3.2 Continuous Descent Approach (CDA) ................................................................................... 108

3.3 Non-Conventional NAVAID Based Procedures (RNAV Approaches) ................................... 109

3.3.1 Overlay Procedures Concept ................................................................................................. 110

3.3.2 Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) .... 111

3.3.3 Sensor Specific Area Navigation (RNAV) Procedures ........................................................... 115

3.3.4 RNP Procedures (Pre-PBN) ................................................................................................... 118

4 THE PERFORMANCE BASED NAVIGATION CONCEPT ................................................... 124

4.1 Description of Performance Based Navigation ...................................................................... 124

4.1.1 Introduction ............................................................................................................................. 124

4.1.2 Navigation Specification ......................................................................................................... 126

4.1.3 NAVAID Infrastructure ............................................................................................................ 132

4.1.4 Navigation Application ............................................................................................................ 132

4.1.5 Future Developments ............................................................................................................. 133

4.2 Airspace Concept ................................................................................................................... 141

4.2.1 Introduction ............................................................................................................................. 141

4.2.2 The Airspace Concept ............................................................................................................ 142

4.2.3 Airspace Concepts by Area of Operation ............................................................................... 143

4.3 Stakeholder Uses of Performance Based Navigation ............................................................ 146

4.3.1 Introduction ............................................................................................................................. 146

4.3.2 Airspace Planning .................................................................................................................. 147

4.3.3 Instrument Flight Procedure Design ....................................................................................... 148

4.3.4 Airworthiness and Operational Approval ................................................................................ 152

4.4 Implementation Guidance ...................................................................................................... 156

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4.4.1 Introduction to Implementation Process ................................................................................. 156

4.4.2 Process 1: Determine Requirements ..................................................................................... 157

4.4.3 Process 2: Identifying the ICAO Navigation Specification for Implementation ...................... 159

4.4.4 Process 3: Planning and Implementation ............................................................................... 161

4.4.5 Guidelines for Development of a New Navigation Specification ............................................ 166

5 CHANGES IN ATS DELIVERY DUE TO PBN IMPLEMENTATION..................................... 169

5.1 ATS Flight Plan Requirements ............................................................................................... 169

5.1.1 Conventional Navigation ........................................................................................................ 171

5.1.2 Non-Conventional Navigation ................................................................................................ 171

5.1.3 Designation of RNAV Routes ................................................................................................. 172

5.2 ATS Procedures ..................................................................................................................... 173

5.2.1 Control Procedures ................................................................................................................ 174

5.2.2 Contingency Procedures ........................................................................................................ 174

5.3 Separation Minima ................................................................................................................. 175

5.3.1 Longitudinal ............................................................................................................................ 175

5.3.2 Lateral..................................................................................................................................... 175

5.4 Mixed Equipage Environment ................................................................................................ 175

5.5 Transition Between Different Operation Environments .......................................................... 176

5.6 Phraseology ........................................................................................................................... 176

5.7 Reporting of Gross Navigational Errors ................................................................................. 176

5.8 RNAV STARs and SIDs ......................................................................................................... 177

5.8.1 Related Control Procedures ................................................................................................... 178

5.8.2 Radar Vectoring Techniques .................................................................................................. 178

5.8.3 Open and Closed STARs ....................................................................................................... 179

5.8.4 Altitude Constraints ................................................................................................................ 180

5.8.5 Descend/Climb Clearances .................................................................................................... 180

5.9 RNP Approach and Related Procedures ............................................................................... 181

5.10 Impact of Requesting a Change to Routing during a Procedure ........................................... 181

5.11 Fix/Waypoint Naming ............................................................................................................. 181

5.12 NAVAID Infrastructure Status Monitoring ............................................................................... 183

5.13 ATS System Monitoring .......................................................................................................... 183

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ABBREVIATIONS

ABAS Aircraft-based augmentation system

ACARS Aircraft Communications Addressing and Reporting System

ADS-B Automatic Dependent Surveillance — Broadcast

ADS-C Automated Dependent Surveillance — Contract

AFM Aircraft Flight Manual

AIP Aeronautical Information Publication

ANSP Air Navigation Service Provider

APV Approach Procedure with Vertical guidance

ATM Air Traffic Management

ATS Air Traffic Service(s)

Baro-VNAV Barometric Vertical NAVigation.

bps Bits per Second

C/A Code Coarse/Acquisition Code

CDGPS Canada-Wide Differential GPS

CDI Course Deviation Indicator

CDU Control and Display Unit

CFIT Controlled Flight Into Terrain

COSPAS Cosmitscheskaja Sistema Poiska Awarinitsch Sudow (Russian: space system for search of vessels in distress)

DGNSS Differential Global Navigation Satellite System

DPGS Differential Global Positioning System

DME Distance Measuring Equipment

DOP Dilution Of Precision

DR Dead Reckoning

DTED Digital Terrain Elevation Data

EASA European Aviation Safety Agency

ECAC European Civil Aviation Conference

ECEF Earth-Centred-Earth-Fixed

EGM 1996 Earth Gravitational Model (EGM96)

ESA European Space Agency

EUROCAE European Organisation for Civil Aviation Equipment

EUROCONTROL European Organisation for the Safety of Air Navigation

FAA Federal Aviation Administration

FAS Final Approach Segment

FDE Fault Detection and Exclusion

FDMA Frequency Division Multiple Access

FMS Flight Management System

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FOC Full Operational Capability

FTE Flight Technical Error

FRT Fixed Radius Transition

GAGAN GNSS Aided GEO Augmented Navigation (India)

GBAS Ground-Based Augmentation System

GEO GEOstationary orbit

GHz GigaHertz

GLONASS GLObal NAvigation Satellite System

GNSS Global Navigation Satellite System

GPS Global Positioning System

GRAS Ground-based Regional Augmentation System

GRS 1980 Geodetic Reference System (GRS80)

HEO Highly Elliptical Orbit

ICAO International Civil Aviation Organisation

IERS The International Earth Rotation and Reference Systems Service

INMARSAT International Maritime Satellite Organisation

INS Inertial Navigation System

IOV In-Orbit Validation

IRNSS Indian Regional Navigation Satellite System

IRS Inertial Reference System

IRU Inertial Reference Unit

JAA Joint Aviation Authorities

L1 The 1575.42 MHz GPS carrier frequency including C/A and P-code

L1C Future GPS L1 civilian frequency

L1F Future Galileo L1 civilian frequency

L2 The L2 civilian code transmitted at the L2 frequency (1227.6 MHz)

L5 The 1176.45 MHz 3rd

civil GPS frequency that tracks carrier at low signal-to-noise ratios

LAAS Local Area Augmentation System

LNAV Lateral NAVigation

Mb Megabit

MB Megabyte

MCDU Multifunction Control and Display Unit

MEL Minimum Equipment List

MHz MegaHertz

MNPS Minimum Navigation Performance Specification

ms millisecond

MSA Minimum Sector Altitude

MTSAT Multi-functional Transport SATellite

NAVAID NAVigation AId (also used as NAVAID)

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NAVSTAR NAVigation Satellite Timing and Ranging (synonymous with GPS)

NM Nautical Mile

NPA Non-Precision Approach

ns nanosecond

NSE Navigation System Error

PA Precision Approach

PBN Performance-Based Navigation

P-code Precision code

PDE Path Definition Error

PE-90 Parameters of the Earth 1990 (see PS90)

POH Pilot Operating Handbook

PPS Precise Positioning Service

PRN# Pseudo-Random Noise Number

PSR Primary Surveillance Radar

PS-90 Parametry Semli 1990 (see PE-90)

RAIM Receiver Autonomous Integrity Monitoring

RF Radius to fix

RNAV Area NAVigation

RNP Required Navigation Performance

RTK Real Time Kinematic

SAR Search And Rescue

SARSAT Search And Rescue Satellite Aided Tracking

SBAS Satellite-Based Augmentation System

SID Standard Instrument Departure

SSR Secondary Surveillance Radar

SNAS Satellite Navigation Augmentation System (China)

SOL Safety-Of-Life

SPS Standard Positioning Service

STAR STandard instrument ARrival

SV Space Vehicle

TLS Target Level of Safety

TSE Total System Error

UHF Ultra High Frequency

UTC Coordinated Universal Time

UTC(SU) Coordinated Universal Time (former Soviet Union, now Russia)

VDB VHF Data Broadcast

VHF Very High Frequency

VNAV Vertical NAVigation

VOR Very high frequency (VHF) Omnidirectional radio Range

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WAAS Wide Area Augmentation System

WGS World Geodetic System

WPT WayPoinT

QSSS Quasi-zenith Satellite System

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EXPLANATION OF TERMS

Absolute Accuracy. In GNSS positioning, absolute accuracy is the degree to which the position of

an object on a map conforms to its correct location on the Earth to an accepted coordinate system.

Acquisition. The process of locking onto a satellite‘s C/A code and P-code. A receiver acquires all

available satellites when it is first powered up, then acquires additional satellites as they become

available and continues tracking them until they become unavailable.

Aircraft-Based Augmentation System (ABAS). An augmentation system that augments and/or

integrates the information obtained from the other GNSS elements with navigation information

available on board the aircraft.

Note: — The most common form of ABAS is receiver autonomous integrity monitoring

(RAIM).

Aircraft Communications Addressing and Reporting System (ACARS). This is a digital data link

system for transmission of short, relatively simple messages between aircraft and ground stations via

radio or satellite. The protocol, which was designed by ARINC to replace their VHF voice service and

deployed in 1978, uses telex formats. SITA later augmented their worldwide ground data network by

adding radio stations to provide ACARS service. ACARS today operates in accordance with the

Aeronautical Telecommunications Network (ATN) protocol for Air Traffic Control communications and

by the Internet Protocol for airline communications.

Airspace concept. An airspace concept provides the outline and intended framework of operations

within an airspace. Airspace concepts are developed to satisfy explicit strategic objectives such as

improved safety, increased air traffic capacity and mitigation of environmental impact etc. Airspace

Concepts can include details of the practical organisation of the airspace and its users based on

particular CNS/ATM assumptions, e.g. ATS route structure, separation minima, route spacing and

obstacle clearance.

Air Navigation Service Provider (ANSP). An Air Navigation Service Provider is the organisation

that separates aircraft both on the ground and in flight in a dedicated block of airspace on behalf of a

state or a number of states. Air Navigation Service Providers are either government departments;

state owned companies, or privatised organisations.

Almanac. A set of orbit parameters that allows calculation of approximate GNSS satellite positions

and velocities. The almanac is used by a GNSS receiver to determine satellite visibility and as an aid

during acquisition of GNSS satellite signals.

Almanac data. A set of data which is downloaded from each satellite over the course of 12.5

minutes. It contains orbital parameter approximations for all satellites, GNSS to universal standard

time (UTC) conversion parameters, and single-frequency ionospheric model parameters.

Antipodal satellites. Antipodal satellites are satellites in the same orbit plane separated by 180° in

argument of latitude.

Anti-spoofing. Denial of the P-code by the control segment is called anti-spoofing. It is normally

replaced by encrypted Y-code.

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Approach Procedure with Vertical guidance (APV). An instrument procedure which utilises lateral

and vertical guidance but does not meet the requirements established for precision approach and

landing operations.

Area Navigation (RNAV). RNAV is a method of navigation that makes possible the operation of an

aircraft on any desired flight path within the coverage of station-referenced navigation aids or within

the limits of the capability of self-contained aids, or a combination of these.

Note: — RNAV systems are divided into two different types;

The first is the “older” more common standard system known simply as a RNAV

System.

The second and more modern type is known as a RNP system.

The fundamental difference between the two is that a RNP System is capable of on-board

navigation performance monitoring and alerting where as the “older” standard RNAV system

does not have these functions.

ATM Community. The aggregate of organisations, agencies or entities that may participate,

collaborate and cooperate in the planning, development, use, regulation, operation and maintenance

of the ATM system.

ATM System. A system that provides ATM through the collaborative integration of humans,

information, technology, facilities and services, supported by air and ground- and/or space-based

communications, navigation and surveillance.

ATS surveillance service. A term used to indicate a service provided directly by means of an ATS

surveillance system.

ATS surveillance system. A generic term meaning variously, ADS-B, PSR, SSR or any comparable

ground-based system that enables the identification of aircraft.

Note: — A comparable ground-based system is one that has been demonstrated, by

comparative assessment or other methodology, to have a level of safety and

performance equal to or better than monopulse SSR.

Baro-VNAV. A navigation system that presents to the pilot computed vertical guidance referenced to

a specified vertical path angle (VPA), nominally 3°. The computer-resolved vertical guidance is based

on barometric altitude and is specified as a VPA from reference datum height (RDH).

Base Station. A GNSS receiver that is employed as the stationary reference. It has a known position

and transmits messages for the rover receiver to use to calculate its position.

Broadcast Ephemerides. A set of parameters which describes the location of satellites with respect

to time, and which is transmitted (broadcast) from satellites.

Canada-Wide Differential Global Positioning System (CDGPS). The CDGPS is a free DGPS

service that is accessible coast-to-coast, throughout most of the continental United States, and into

the Arctic.

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Coarse Acquisition (C/A) code. A pseudo-random string of bits that is used primarily by commercial

GNSS receivers to determine the range to the transmitting GNSS satellite. The 1023 chip GPS C/A

code repeats every 1 mili-second giving a chip length of 300 m, which is very easy to lock onto.

Collaborative Decision Making (CDM). In the South African ATM context CDM will be understood

as meaning the following;

A process of collaboratively considering alternative understandings of a problem, an issue or a topic,

whilst recognising competing interests, priorities or constraints. Fundamental to this process is a

requirement to articulate in a concise and agreed upon manner the problem, issue or topic. This

process is aimed at improving the ATM system through increased information exchange among and

brings together the various parties in the ATM community. This process will result in an agreed to

application of the most appropriate action.

Control Segment. The master control station and the globally dispersed reference stations used to

manage the GNSS satellites, determine their precise orbital parameters, and synchronise their clocks.

Coordinated Universal Time (UTC). This time system uses the second-defined true angular rotation

of the Earth measured as if the Earth rotated about its Conventional Terrestrial Pole. However, UTC is

adjusted only in increments of one second. The time zone of UTC is that of Greenwich Mean Time

(GMT).

Dead Reckoning. The process of determining a vessel‘s approximate position by applying (DR) from

its last known position a vector or a series of consecutive vectors representing the run that has since

been made, using only the courses being steered, and the distance run as determined by log, engine

rpm, or calculations from speed measurements.

Differential GNSS (DGNSS). A technique to improve GNSS accuracy that uses pseudo-range errors

at a known location to improve the measurements made by other GNSS receivers within the same

general geographic area.

Dilution of Precision (DOP). A numerical value expressing the confidence factor of the position

solution based on current satellite geometry. The lower the value, the greater the confidence in the

solution. DOP can be expressed in the following forms:

GDOP: Uncertainty of all parameters (latitude, longitude, height, clock offset)

PDOP: Uncertainty of 3-D parameters (latitude, longitude, height)

HTDOP: Uncertainty of 2-D and time parameters (latitude, longitude, time)

HDOP: Uncertainty of 2-D parameters (latitude, longitude)

VDOP: Uncertainty of height parameter

TDOP: Uncertainty of clock offset time parameter

Doppler. The change in frequency of sound, light, or other wave caused by movement of its source

relative to the observer.

Theoretical Doppler: The expected Doppler frequency based on a satellite‘s motion relative

to the receiver. It is computed using the satellite‘s co-ordinates and velocity, and the

receiver‘s co-ordinates and velocity.

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Apparent Doppler: Same as Theoretical Doppler of satellite above, with clock drift correction

added.

Instantaneous Carrier: The Doppler frequency measured at the receiver, at the epoch.

Earth-Centred-Earth Fixed (ECEF). This is a co-ordinate system which has the X-axis in the Earth‘s

equatorial plane pointing to the Greenwich prime meridian, the S-axis pointing to the North Pole, and

the Y-axis in the equatorial plane 90° from the X-axis with an orientation which forms a right-handed

XYS system.

Ephemeris. A set of satellite orbit parameters that are used by a GNSS receiver to calculate precise

GNSS satellite positions and velocities. The ephemeris is used in the determination of the navigation

solution and is updated periodically by the satellite to maintain the accuracy of GNSS receivers.

Ephemeris data. The data down-linked by a GNSS satellite describing its own orbital position with

respect to time.

Epoch. Strictly a specific point in time. Typically when an observation is made.

Fault Detection and Exclusion (FDE). Fault detection and exclusion is a function performed by

some GNSS receivers. This function is designed to detect the presence of a faulty satellite signal and

to then exclude it from the position calculation.

Flight Management System (FMS). An integrated system consisting of an airborne sensor, receiver

and computer with both navigation and aircraft performance databases, which provides aircraft

performance and RNAV guidance to a display and automatic flight control system (autopilot).

Flight Technical Error (FTE). The accuracy with which an aircraft is controlled, as measured by the

indicated aircraft position with respect to the indicated command or desired position. It does not

include blunder errors.

Note: — FTE is sometimes referred to as path steering error (PSE).

Fixed Radius Path (FRP). A fixed radius path is a type of RNAV System Leg. Fixed radius paths

take two forms, the radius to fix (RF) and the fixed radius transition (FRT). These FRPs legs are used

in en-route and terminal procedure design to increase the capacity of a specific portion of airspace.

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Fixed Radius Transition (FRT). The fixed radius transition leg may be employed when there is a

requirement for a curved path to be used during en-route procedure design. The FRT leg is defined

by radius, arc length and a fix.

RNP systems capable of ―flying‖ this leg type, are also capable of conforming to the same track-

keeping accuracy during the turn as in a straight line segments in accordance with the navigation

specification published for the portion of airspace within which this manoeuvre is required.

Bank angle limits for different aircraft types and winds aloft are taken into account in procedure

design. This turn has two possible radii, 22.5 NM for high altitude routes (above FL195) and 15

NM for low altitude routes. Using such path elements in a RNAV route enables improvement in

airspace usage through more efficient and reduced spacing between parallel routes.

Flexible Use of Airspace (FUA). Within the context of this document, FUA is understood to mean;

Airspace is no longer designated as purely "civil" or "military" airspace, but considered as one

continuum and allocated according to user requirements. This allocation will done by the ANSP and in

accordance with an agreed to CDM process. Any necessary airspace segregation is temporary and

based on real-time usage within a specific time period. Contiguous volumes of airspace are not

constrained by national boundaries.

Flight profile. The flight path of an aircraft expressed in terms of altitude, speed, range, time and

manoeuvre.

Galileo. Galileo will be the European Union‘s own global navigation satellite system, providing a

highly accurate, guaranteed global positioning service under civilian control. The fully deployed

Galileo system will consist of 30 satellites (27 operational + 3 active spares), positioned in three

circular orbits, 23 616 km above the Earth, and at an inclination of the orbital planes of 56° with

reference to the equatorial plane.

Gate to Gate. A concept where the air traffic operations of ATM community members are such that

the successive planning and operational phases of their processes are managed and can be

achieved in a seamless and coherent manner.

Geocentric. Relating to, measured from, or with respect to the centre of mass of the Earth.

Geodetic System. Geodetic systems or geodetic data are used in geodesy, navigation, surveying by

cartographers and satellite navigation systems to translate positions calculated in terms of X, Y and S

coordinate models into conventional latitude and longitude position.

Ground-Based Augmentation System (GBAS). A ground-based augmentation system is a system

that supports wide-area or regional augmentation through the use of additional satellite-broadcast

messages. Such systems are commonly composed of multiple ground stations, located at accurately-

surveyed points. The ground stations take measurements from one or more of the GNSS satellites,

the satellite signals, or other environmental factors which may impact the signal received by the

users. Using these measurements, information messages are created and sent to one or more

satellites for broadcast to the end users. Generally, GBAS networks are considered localised,

supporting receivers within 20km, and transmitting in the very high frequency (VHF) or ultra high

frequency (UHF) bands.

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Geo-stationary. A satellite orbit along the equator that results in a constant fixed position over a

particular reference point on the Earth‘s surface.

Global Navigation Satellite System (GLONASS). GLONASS is a radio satellite navigation system,

the Russian counterpart to the United States‘ GPS and European Union‘s Galileo positioning

systems. When complete, the GLONASS space segment will consist of 24 satellites in 3 orbital

planes, with eight satellites per plane. The satellites are placed into nominally circular orbits with

target inclinations of 64.8° and an orbital height of about 19 140 km, which is about 1 050 km lower

than GPS satellites.

Global Navigation Satellite Systems (GNSS). GNSS is the standard generic term for satellite

navigation systems (Sat Nav) that provide autonomous geo-spatial positioning with global coverage.

GNSS allows small electronic receivers to determine their location (longitude, latitude, and certain

receivers also altitude) to within a few meters using time signals transmitted along a line-of-sight by

radio from satellites. Receivers calculate the precise time as well as their position, which can be used

as a reference in navigation computers.

The Global Positioning System (GPS) is a space-based global navigation satellite system that

provides reliable location and time information in all weather and at all times and anywhere on or near

the Earth where there is an unobstructed line of sight to four or more GPS satellites. It is maintained

by the United States government and is freely accessible by anyone with a GPS receiver.

Ground-Based Regional Augmentation System (GRAS). Each of the terms, ground-based

augmentation system (GBAS) and ground-based regional augmentation system (GRAS) describe a

system that supports augmentation through the use of terrestrial radio messages. As with the satellite

based augmentation systems, ground-based augmentation systems are commonly composed of one

or more accurately surveyed ground stations, which take measurements concerning the GNSS, and

one or more radio transmitters, which transmit the information directly to the end user. GRAS is

applied to systems that support a larger (more than 20km), regional area, and transmit in the VHF

bands.

INMARSAT. INMARSAT plc. is a British satellite telecommunications company, offering global,

mobile services. It provides telephony and data services to users worldwide, via portable or mobile

terminals which communicate to ground stations through eleven geosynchronous telecommunications

satellites. Inmarsat's network provides communications services to a range of governments, aid

agencies, media outlets and businesses with a need to communicate in remote regions or where

there is no reliable terrestrial network.

An Inertial Navigation System (INS) is a navigation aid that uses a computer, motion sensors

(accelerometers) and rotation sensors (gyroscopes) to continuously calculate via dead reckoning the

position, orientation, and velocity (direction and speed of movement) of a moving object without the

need for external references. It is used on vehicles such as ships, aircraft, submarines, guided

missiles, and spacecraft. Other terms used to refer to inertial navigation systems or closely related

devices include inertial guidance system, inertial reference platform, inertial instrument, and many

other variations.

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Lateral Navigation (LNAV). LNAV refers to navigating over a ground track with guidance from an

electronic device which gives the pilot (or autopilot) error indications in the lateral plane only and not

in the vertical plane. In aviation lateral navigation is one of two guidance types: linear guidance and

angular guidance.

Linear guidance means that the actual position of the aircraft, i.e. the deviation left or right of the

desired ground track is available as a distance.

In angular guidance, the error indication is given in degrees of arc from the desired line relative to

a ground-based navigation device.

To provide an illustration, as the aircraft approaches the ground-based navigation device whilst

maintaining a constant angular error, the aircrafts distance from the desired ground line

decreases. In the context of aviation instrument approaches, an LNAV approach (one that uses

lateral navigation) is implied to be a approach using GNSS as the primary navigation source and

to have linear lateral guidance. A VOR based approach will have angular lateral guidance.

The FMS mode is normally called LNAV or Lateral Navigation for the lateral flight plan. LNAV

provides roll steering command to the autopilot and VNAV provides speed and pitch or altitude

targets.

L-band. L-band is a frequency range between 390 MHz and 1.55 GHz which is used for satellite

communications and for terrestrial communications between satellite equipment. L-band includes

GNSS carrier frequencies L1, L2, CDGPS and the Omni-STAR satellite broadcast signal.

Minimum Navigation Performance Specification (MNPS). A specified set of minimum navigation

performance standards which aircraft must meet in order to operate in MNPS designated airspace. In

addition, aircraft must be certified by their State of Registry for MNPS operation. The objective of

MNPS is to ensure the safe separation of aircraft and to derive maximum benefit, generally through

reduced separation standards, from the improvement in accuracy of navigation equipment developed

in the recent years.

Mixed navigation environment. An environment where different navigation specifications may be

applied within the same airspace (e.g. RNP 10 routes and RNP 4 routes in the same airspace) or

where operations using conventional navigation are allowed in the same airspace with RNAV or RNP

applications.

Multipath Errors. GNSS positioning errors caused by the intersection of the satellite signal and its

reflections.

Nanosecond. 1 x 10-9

second.

Navigation aid (NAVAID) infrastructure. NAVAID infrastructure refers to space-based and/or

ground-based navigation aids available to meet the requirements in the navigation specification.

Navigation application. The application of a navigation specification and the supporting NAVAID

infrastructure, to routes, procedures, and/or defined airspace volume, in accordance with the intended

airspace concept.

Note: — The navigation application is one element, along with communication, surveillance

and ATM procedures which meet the strategic objectives in a defined airspace

concept.

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Navigation function. The detailed capability of a navigation system (such as the execution of leg

transitions, parallel offset capabilities, holding patterns, navigation databases) required to meet an

airspace concept requirement.

Note: — Navigational functional requirements are one of the drivers for the selection of a

particular navigation specification. Navigation functionalities (functional

requirements) for each navigation specification can be found in Volume II, Parts B

and C of the Performance-Based Navigation (PBN) Manual (Doc 9613).

Navigation specification. A set of aircraft and aircrew requirements needed to support

Performance-Based Navigation operations within a defined airspace. There are two kinds of

navigation specification:

RNAV specification. A navigation specification based on area navigation that does not include the

requirement for performance monitoring and alerting, designated by the prefix RNAV, e.g. RNAV

5, RNAV 1 and

RNP specification. A navigation specification based on area navigation that includes the

requirement for performance monitoring and alerting, designated by the prefix RNP, e.g. RNP 4,

RNP APCH.

Note: — The Performance-Based Navigation (PBN) Manual (Doc 9613), Volume II, contains

detailed guidance on navigation specifications.

Navigation System Error (NSE). This is the root-sum-square (RSS) of the ground station error

contribution, the airborne receiver error and the display system contribution.

Note: — NSE is sometimes referred to as position estimation error (PEE).

Non-Precision Approach. An instrument approach procedure which utilises lateral guidance but

does not utilise vertical guidance.

Note: — Lateral and vertical guidance refers to the guidance provided either by a ground-

based navigation aid or computer-generated navigation data.

Oblate Spheroid. If an ellipse is rotated about its minor axis, the result is an oblate (flattened)

spheroid, like a lentil.

Omni-STAR. A wide-area GNSS correction service, using L-band satellite broadcast frequencies

(1525 – 1560 MHz). Data from many widely-spaced Reference Stations is used in a proprietary multi-

site solution. Omni-STAR Virtual Base Station types achieve sub-metre positioning over most land

areas worldwide while Omni-STAR High Performance (HP) types achieve 10 cm accuracy. Use of the

Omni-STAR service requires a subscription.

Path Definition Error (PDE). The distance between the defined path and the desired path at a

specific point and time.

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P-code. Precise code or protected code. A pseudo-random string of bits that is used by GPS

receivers to determine the range to the transmitting GPS satellite. P-code is replaced by an encrypted

Y-code when anti-spoofing is active. Y-code is intended to be available only to authorised (primarily

military) users.

Performance-Based Navigation (PBN). Area navigation based on performance requirements for

aircraft operating along an ATS route, on an instrument approach procedure or in a designated

airspace.

Note: — Performance requirements are expressed in navigation specifications in terms of

accuracy, integrity, continuity, availability and functionality needed for the proposed

operation in the context of a particular airspace concept.

Perigee. The point in a body‘s orbit at which it is nearest the Earth.

Precise Positioning Service (PPS). The GNSS positioning, velocity, and time service which is

available on a continuous, worldwide basis to users authorised by the US Department of Defence

(typically using P-code).

Procedural control. Air traffic control service provided by using information derived from sources

other than an ATS surveillance system.

Precision Approach. An instrument approach procedure using precision lateral and vertical

guidance with minima as determined by the aircraft approach category.

Note: — Lateral and vertical guidance refers to the guidance provided either by a ground-

based navigation aid or computer-generated navigation data.

Pseudo-random Noise Number (PRN#). A number assigned by the GPS system designers to give

a set of pseudo-random codes. Typically, a particular satellite will keep its PRN (and hence its code

assignment) indefinitely, or at least for a long period of time. It is commonly used as a way to label a

particular satellite.

Pseudo-range. The calculated range from the GNSS receiver to the satellite determined by taking

the difference between the measured satellite transmit time and the receiver time of measurement

and multiplying it by the speed of light. This contains several sources of error.

Pseudo-range measurements. Measurements made using one of the pseudo-random codes on the

GNSS signals. They provide an unambiguous measure of the range to the satellite including the effect

of the satellite and user clock biases.

PS-90. Parametri Semli 1990 (PS-90, or in English translation, Parameters of the Earth 1990, PE-90)

geodetic datum. GLONASS information is referenced to the PS-90 geodetic datum and GLONASS

co-ordinates are reconciled in some GLONASS-capable GNSS receivers through a position filter and

output to WGS-84.

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Radius to fix (RF). The radius to fix leg type may be employed when there is a requirement for a

curved path to be used during terminal or approach procedure design. The RF leg is defined by

radius, arc length and a fix.

RNP systems capable of ―flying‖ this leg type, are also capable of conforming to the same track-

keeping accuracy during the turn as in a straight line segments in accordance with the navigation

specification published for the portion of airspace within which this manoeuvre is required.

Bank angle limits for different aircraft types and winds aloft are taken into account in procedure

design. This turn has two possible radii, 22.5 NM for high altitude routes (above FL195) and 15

NM for low altitude routes. Using such path elements in a RNAV route enables improvement in

airspace usage through more efficient and reduced spacing between parallel routes.

Receiver Autonomous Integrity Monitoring (RAIM). A form of ABAS whereby a GNSS receiver

processor determines the integrity of the GNSS navigation signals using only GPS signals or GPS

signals augmented with altitude (baro-aiding). This determination is achieved by a consistency check

among redundant pseudo-range measurements. At least one additional satellite needs to be available

with the correct geometry over and above that needed for the position estimation, for the receiver to

perform the RAIM function.

Real-Time Kinematic (RTK). A type of differential positioning based on observations of a carrier

phase.

Required Navigational Performance (RNP). A statement of the navigation performance necessary

for operations within a defined Airspace.

RNAV Approach. A generic term used to describe instrument approach procedures that rely on

aircraft area navigation equipment (the Flight Navigation Computer - FNC component of the Flight

Management System - FMS) for navigation guidance. RNAV approach procedures are designated

and utilised as follows;

RNAV (GNSS). The current European Non-Precision RNAV instrument approach application.

RNAV 1. PBN SIDs and STARs and Instrument Approach Procedures up to the final approach fix.

RNAV 2. PBN SIDs and STARs and Instrument Approach Procedures up to the final approach fix.

RNP 2. Future development.

Basic-RNP 1. PBN SIDs and STARs.

Advanced-RNP 1. Future development.

RNP APCH. PBN Instrument Approach Procedure and the current RNAV (GNSS) Non-Precision

RNAV Instrument Approach Procedures. RNP APCH is defined as a RNP approach procedure

that requires a lateral TSE of +/- 1 NM in the initial, intermediate and missed approach segments

and a lateral TSE of +/- 0.3 NM in the final approach segment.

RNP AR APCH. PBN Instrument Approach Procedure. RNP AR APCH is defined as a RNP

approach procedure that requires a lateral TSE as low as +/- 0.1 NM on any segment of the

approach procedure. RNP AR APCH procedures also require that a specific vertical accuracy be

maintained as detailed in The Performance-Based Navigation (PBN) Manual (Doc 9613), Volume

II, Chapter 6.

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RNAV operations. This refers to aircraft operations where the navigation of the aircraft is achieved

using the RNAV method of navigation (in this instance the navigation function is achieved through

automated means i.e. the use of a standard RNAV system without the ability to perform on-board

navigation performance monitoring and alerting).

RNAV Route. An ATS route established for the sole use of aircraft capable of employing RNAV in

accordance with a prescribed RNAV navigation specification.

RNAV system. This refers to a flight navigation computer that enables the application of the RNAV

method of navigation through automated means without the ability to perform on-board navigation

performance monitoring and alerting. A RNAV system may be and most often is included as part of a

Flight Management System (FMS).

RNAV system Leg. The path between two waypoints.

RNP operations. This refers to aircraft operations where the navigation of the aircraft is achieved

using the RNAV method of navigation (in this instance the navigation function is achieved through

automated means i.e. the use of a RNP system and thus includes the ability to perform on-board

navigation performance monitoring and alerting).

RNP route. An ATS route established for the sole use of aircraft adhering to a prescribed RNP

navigation specification.

RNP system. This refers to a flight navigation computer that enables the application of the RNAV

method of navigation through automated means and thus includes the ability to perform on-board

navigation performance monitoring and alerting. RNP systems are only available as integral

components of Flight Management Systems (FMS).

Rover Station. The GNSS receiver which does not know its positions and needs to receive

measurements from a base station to calculate differential GNSS positions (the terms remote and

rover are interchangeable).

Safety-of-Life (SOL). The safety-of-life service will be offered to Galileo users who are highly

dependent on precision, signal quality and signal transmission reliability (typically commercial

aviation). It will offer a high level of integrity and consequently, provide the user with a very rapid

warning of any possible malfunctions. The SOL service will be transmitted in two frequency bands. On

the L1 at 1575.42 MHz and on E5a+E5b at 1207.14 MHz. Users may receive signals from two

frequency bands independently.

Satellite-Based Augmentation System (SBAS). A wide coverage augmentation system in which

the user receives augmentation information from a satellite-based transmitter.

Selected Availability (SA). The method used in the past by the US Department of Defence to

control access to the full accuracy achievable by civilian GPS equipment (generally by introducing

timing and ephemeris errors).

Selected Waypoint. The waypoint currently selected to be the point toward which the vessel is

travelling. Also called ―to‖ waypoint, destination or destination waypoint.

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Sidereal Day. A sidereal day is the rotation of the Earth relative to the equinox and is equal to one

calendar day (the mean solar day) minus approximately 4 minutes.

Spheroid. A spheroid, or ellipsoid of revolution is a quadric surface obtained by rotating an ellipse

about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters.

Standard Instrument Arrival (STAR). A designated instrument flight rule arrival route linking a

significant point, normally on an ATS route, with a point from which a published instrument approach

procedure can be commenced.

Standard Instrument Departure (SID). A designated instrument flight rule departure route linking

the aerodrome or a specified runway of the aerodrome with a specified significant point, normally on a

designated ATS route, at which the en-route phase of a flight commences.

Standard Positioning Service (SPS). A positioning service made available by the US Department of

Defence which is available to all GPS civilian users on a continuous, worldwide basis (typically using

C/A code).

Space Vehicle ID (SV). Sometimes used as SVID. A unique number assigned to each satellite for

identification purposes. The ―space vehicle‖ is a GNSS satellite.

Total System Error (TSE). The difference between the true position and desired position of an

aircraft. This error is equal to the vector sum of the path steering error, path definition error and

position estimation error. In the lateral dimension, a combination of navigation system error, RNAV

computation error, display system error and FTE. In the longitudinal dimension, a combination of

navigation system error, RNAV computation error and display system error.

Trajectory. This is a description of the movement of an aircraft, both in the air and on the ground,

including position, time and, at least via calculation, speed and acceleration.

Vertical Navigation (VNAV). Vertical Navigation in aviation is a function of an autopilot which directs

vertical movement of aircraft according to a pre-programmed FMS flight path during cruise, according

to the ILS glide slope during a conventional precision approach or more recently according to a pre-

programmed FMS flight path during a RNAV approach. Guidance includes control of the pitch axis

and control of the throttle.

Waypoint. A specified geographical location used to define an ATS route.

A waypoint is defined as a geographic coordinate (in WGS84) and is identified either:

by a 5 letter unique name code, e.g. BARNA, or

if located with a ground-based NAVAID by the 3 letter ICAO identifier for that station, e.g. OTR, or

in Terminal Airspace only, by an alphanumeric name code, e.g. DF410.

World Geodetic System 1984 (WGS-84). An ellipsoid designed to fit the shape of the entire Earth

as well as possible with a single ellipsoid. It is often used as a reference on a worldwide basis, while

other ellipsoids are used locally to provide better fit to the Earth in a local region. GNSS uses the

centre of the WGS-94 ellipsoid as the centre of the GNSS ECEF reference frame.

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Y-code. An encrypted form of P-code. Satellites transmit Y-code in place of P-code when anti-

spoofing is in effect.

4D RNAV. 4D RNAV is a concept that has developed as the application of RNAV evolved. This

development progressed from 2D RNAV to 3D RNAV to 4D RNAV and may be explained as follows;

2D RNAV encompasses the application of RNAV capabilities in the horizontal plane only;

3D RNAV indicates the addition of a guidance capability in the vertical plane (providing profile

guidance) to the 2D RNAV capabilities; and

4D RNAV indicates the addition of a time function (giving time guidance) to 3D RNAV

capabilities.

4D Trajectory. A four-dimensional (x, y, z and time) trajectory of an aircraft from gate-to-gate, at the

level of fidelity required for attaining the agreed ATM System performance levels.

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1 AREA NAVIGATION (RNAV) SYSTEMS.

1.1 Background

The ability to navigate an aircraft has been a fundamental component of flying from the day the Wright

Brothers made their first flight. Since that first powered flight, flying and navigating aircraft has

developed exponentially. This chapter will discuss the development of this near mythical thing termed

aircraft navigation, aka area navigation.

The first few flights ever undertaken where made during daylight, clear of any cloud and precipitation

and with the pilot seeing where he was flying (visual navigation). Very soon the potential of

commercial air travel was identified and with this came the realisation that aircraft would have to be

flown and thus navigated by night and during adverse weather conditions. This ushered in the

concept of ―all weather operations‖.

Early public transport operation relied on radio beacons, intermittent two way communication with Air

Traffic Control (ATC) and a very basic airway infrastructure. The limited level of Air Traffic Service

(ATS) was based on what we now know as procedural control, requiring and limiting aircraft to fly

either directly to or away from ―beacons‖ (VOR or NDB ground stations). Very soon after the start of

public air transport operations, aircraft were being operated, but for takeoff and landing, entirely

without visual reference to the ground. Navigation was effected by sole reference to radio beacons

and this process came to be known as Radio Navigation. Radio Navigation enabled the early

navigators to manually plot the aircraft position, calculate ground speed and estimated time of arrival

and plot a required course to any point on their maps. This ―new‖ technique was called Area

Navigation and was based on Radio Navigation. Soon these two concepts became synonymous one

with the other and were simply referred to as RNAV. The accepted meaning of the abbreviation RNAV

being Area Navigation. Advances in technology meant that the navigation function could be

performed by a purpose built Flight Navigation Computer (FNC). The FNC would eventually be

incorporated into the aircraft systems management computer know as the Flight Management System

(FMS), thus replacing the human flight navigator.

The continuing growth in aviation increased the demands on airspace capacity and therefore

emphasised the need for optimum utilisation of available airspace. Improved operational efficiency

derived from the application of RNAV techniques resulted in the development of navigation

applications in various regions worldwide and for all phases of flight. Requirements for RNAV

applications on specific routes and/or within specific airspaces where defined. This was an attempt to

ensure that flight crews and air traffic controllers (ATCs) were aware of the on-board RNAV system

capabilities. This was not entirely successful and largely failed to achieve the anticipated financial

benefits of RNAV as was initially identified. RNAV systems evolved in a manner similar to but much

faster than conventional ground-based routes and procedures. Air Navigation Service Providers

(ANSPs) and Civil Aviation Authorities would identify a specific RNAV system, its performance would

be evaluated through a combination of analysis and flight testing and then it would be approved for a

specific procedure in a specific portion of airspace. For domestic operations, the initial RNAV systems

used very high frequency omnidirectional radio range (VOR) and distance measuring equipment

(DME) for estimating their position; for oceanic operations, Inertial Navigation Systems (INS) were

employed. These ―new‖ systems were developed, evaluated and certified. Airspace and obstacle

clearance criteria were developed based on the performance of available equipment and

specifications for requirements were based on available capabilities. In some cases, it was necessary

to identify the individual models of equipment that could be operated within the airspace concerned.

Such prescriptive requirements resulted in delays to the introduction of new RNAV system capabilities

and higher costs for maintaining appropriate certification. To avoid such prescriptive specifications of

requirements, the Performance-Based Navigation (PBN) Implementation Manual introduces an

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alternative method for defining equipage requirements by specifying the navigation performance

requirements.

1.1.1 Conventional Navigation Methods and Procedures

This new concept of all weather operations meant that some means of navigation at night and

during adverse weather condition had to be developed, i.e. navigating without any visual

reference to the ground whatsoever. The earliest developments resulted in the wide spread

application of what we now refer to as ground-based navigation aids (NAVAIDs – VORs &

NDBs). These ground-based NAVAIDs would prove to be plagued with limitations, some of

these are briefly reviewed below.

a. NAVAIDs.

Early radio navigation (area navigation aka RNAV) was accomplished with reference to either

radio beacons (NDBs, VORs and DMEs) on the ground or on-board self-contained systems

(Inertial Navigation Systems - INS). The ground-based NAVAIDs had to have airborne

counterparts, these are named as follows;

Ground-Based NAVAID Airborne Counterpart

VOR VOR

DME DME

NDB ADF

i. Accuracy.

Conventional NAVAIDs suffers from various errors, the NDB for instance suffers from a

number of errors mostly related to atmospheric conditions. The VOR is less susceptible to

these errors but is still restricted to line of sight. Both the NDB and VOR have the further

disadvantage of radiation accuracy issues, in that any errors introduced at the station will be

magnified with increased distance away from the station. The single most significant error

associated with the NDB and VOR may be termed ―splay errors‖. This describes the inherent

area of uncertainty that results from the

inaccurate radial definition by a VOR station or in

the case of an NDB/ADF, the inaccurate

determination of the bearing to the NDB. The

DME is more accurate than both the NDB and

VOR in terms of signal (position line) definition in

that it does not suffer from this inherent ―splay

error‖ but due to the operating method a DME

station is limited to supporting distance

calculation by a maximum of 100 airborne DME

platforms at any one time (the 100 strongest

interrogations rather than the 100 closest

aircraft). Due to its inherent limitations,

susceptibility to interference and inaccurate

bearing definition capability the NDB/ADF was

eliminated very early on as a possible navigation

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signal input to any FNC (now referred to as RANV system). To date multiple simultaneous

DME signal inputs to RNAV systems provide the most accurate and cost effective navigation

solution where high accuracy is required from RNAV systems.

ii. Range.

Older NDBs had very limited range while some marine beacons and more modern NDBs are

more powerful. VOR stations may be received at distances as great a 200 NM but at this

distance the lateral accuracy due to the increasing ―splay error effect‖ is much reduced. DME

stations may be used at distances as large as 200 NM and will maintain their accuracy at

maximum range (i.e. DME range arc definition accuracy).

b. Displays.

ADF

DME

ADF

VOR

i. Accuracy

Conventional NAVAID displays all suffer from mechanical errors. These were all analogue

systems that were linked to mechanical display unit. Due to this fact these displays suffered

from a significant display error. Later DME display units had a digital display that practically

eliminated any display error. With the development of the ―glass cockpit‖ the display errors of

the VOR were also greatly reduced.

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c. Plotting

Initially a flight navigator would perform a manual

plot using the signals from radio beacons. These

bearings (to an NDB), radials (from a VOR) and

DME range arcs (from a DME ground station)

would be plotted. This process, though not

necessarily difficult but rather mundane and

repetitive, was prone to errors. Lack of attention

to detail by the navigator would result in an

inaccurate plot and thus the aircraft may be

allowed to drift significantly far off course before

an

effective correction was made. Again as a result

of increased operation demand and advances in

technology this manual plotting function would

ultimately be performed by a FNC. The FNC was

able to ensure a repeatable plotting performance,

both in terms of accuracy and reliability. Early

FNCs were not certified in any way but later

application of RNAV saw the introduction of

Required Navigation Performance (RNP)

accuracy as an attempt to standardise and

guarantee the accuracy and repeatability of

accurate navigation performance.

i. Position Fixing

The fundamental aim of navigation is to

accurately, reliably and consistently determine

and/or know the position of an aircraft in flight.

Using navigation signal inputs (NDB, VOR, DME

and GNSS) the accuracy of the plotting solution

is largely determined by the geometry of the plot.

Two position lines (each with an accepted

definition accuracy of 5 - the ICAO standard for

the VOR) will produce a fairly well defined

position. If the same two position line intersected

at a smaller angle, the position will be less well

defined. This position definition will reduce in

clarity as the intersecting angle of the two

position lines reduces.

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1.1.2 RNAV Navigation Methods and Procedures

a. Manual Area Navigation (RNAV).

The process performed by a flight navigator whereby the manual tuning of VOR, DME and

ADF frequencies, physical drawing of position lines from ground-based radio beacons on a

plotting chart is carried out, may be termed manual area navigation. This process enables

the navigation of an aircraft along any desired/required track within the coverage area of the

selected and tuned-in navigation radio beacons. The accuracy of this process is affected by a

number of factors and these include but are not limited to the radio beacon signal definition

accuracy and the accuracy of the manual plotting by the navigator. The basic process of

manual plotting is a fairly laborious process and thus will have a limit in terms of its

applicability with an increase in either aircraft speed and/or complexity of route.

b. Automated Area Navigation (RNAV).

This is where the navigation function (plotting to determine aircraft position) is performed by a

FNC. The navigation solution i.e. the aircraft position, is presented to the pilot on either/or

both the CDI/(E)HSI and the Primary Navigation Display. The accuracy of this process is

affected by the radio beacon signal definition accuracy but the possible error introduced by

the human skill factor is removed. Here the

processing method of the FNC does have a small

influence on the overall navigation accuracy while the

impact of aircraft speed and route complexity has

been mitigated. In the most recent applications of

RNAV it has been found that the processing method

of different FNCs result in differing navigation

performances in terms of track keeping during turns.

This will be discussed later under the headings of

Fixed Radius Transitions (FRTs) and Radius to Fix

(RF) RNAV system leg types. Automated RNAV or

RNAV Systems today use any one or combination of

navigation signal inputs. These are DME/DME,

VOR/DME, INS and more recently GNSS.

1.1.3 WGS - 84 Geodetic Reference Datum

The Earth is not a perfect sphere, it is now believed that the Earth looks more like an egg

rather than a ball. This odd shape was discovered due to the ongoing geographic surveys

conducted globally. Historically a number of different means and approaches have been used

during these surveys.

The World Geodetic System (WGS) is a standard survey reference method (mathematical

model of the Earth) for use in cartography, geodesy, and navigation. It comprises a standard

coordinate frame for the Earth, a standard spheroidal reference surface (the datum or

reference ellipsoid) for raw altitude data, and a gravitational equipotential surface (the geoid)

that defines the nominal sea level.

Because of the combined effects of gravitation and rotation, the Earth's shape is roughly that

of a sphere slightly flattened at the poles. For that reason, in cartography the shape of the

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Earth is often approximated by an oblate spheroid instead of a sphere. The current World

Geodetic System model, in particular, uses a spheroid whose radius is approximately

6,378.137 km at the equator and 6,356.752 km at the poles (a difference of over 21 km). The

latest revision is WGS 84 (dating from 1984 and last revised in 2004), which will be valid up to

about 2010. Earlier schemes included WGS 72, WGS 66, and WGS 60. WGS 84 is the

reference coordinate system used by the Global Positioning System. The coordinate origin of

WGS 84 is located at the Earth's centre of mass; the error is believed to be less than 2 cm.

In WGS 84, the meridian of zero longitude is the International Earth Rotation and Reference

Systems Service (IERS) Reference Meridian. It lies 5.31 arc seconds east of the Greenwich

Prime Meridian, which corresponds to 102.5 meters (336.3 feet) at the latitude of the Royal

Observatory. As of the latest revision, the WGS 84 datum surface is a pole-flattened (oblate)

spheroid, with major (transverse) radius a = 6,378,137 m at the equator, and minor

(conjugate) radius b = 6,356,752 m at the poles (a flattening of 21.384 685 755 km, or

1/298.257 223 563 ≈ 0.335% in relative terms). The b parameter is often rounded to

6,356,752.3 m in practical applications.

The 1980 Geodetic Reference System (GRS80) posted a 6,378,137 m semi-major axis and a

1:298.257 flattening. This system was adopted at the XVII General Assembly of the

International Union of Geodesy and Geophysics (IUGG). It is essentially the basis for

geodetic positioning by the Global Positioning System and is thus also in extremely

widespread use outside the geodetic community.

Presently WGS 84 uses the 1996 Earth Gravitational Model (EGM96) geoid, revised in 2004.

The deviations of the EGM96 geoid from the WGS 84 reference ellipsoid range from about -

105 m to about +85 m. EGM96 differs from the original WGS 84 geoid, referred to as EGM84.

In the early 1980s the need for a new world geodetic system was generally recognised by the

geodetic community, also within the US Department of Defence. WGS 72 no longer provided

sufficient data, information, geographic coverage, or product accuracy for all the then current

and anticipated applications. The means for producing a new WGS were available in the form

of improved data, increased data coverage, new data types and improved surveying

techniques. GRS 80 parameters together with available Doppler, satellite laser ranging and

Very Long Baseline Interferometry (VLBI) observations constituted significant new

information. An outstanding new source of data had become available from satellite radar

altimetry. Also available was an advanced least squares method called collocation which

allowed for a consistent combination solution from different types of measurements all relative

to the Earth's gravity field, i.e. geoid, gravity anomalies, deflections, dynamic Doppler, etc.

The WGS 84 originally used the GRS 80 reference ellipsoid, but has undergone some minor

refinements in later editions since its initial publication. Most of these refinements are

important for high-precision orbital calculations for satellites but have little practical effect on

typical topographical uses.

The new World Geodetic System was called WGS 84. It is currently the reference system

being used by the Global Positioning System. It is geocentric and globally consistent within

±1 m. Current geodetic realisations of the geocentric reference system family International

Terrestrial Reference System (ITRS) maintained by the IERS are geocentric, and internally

consistent, at the few-cm level, while still being meter-level consistent with WGS 84.

1.1.4 Historical Overview – Future Air Navigation System (FANS)

Air Traffic Control's ability to monitor aircraft has always been outpaced by the growth of flight

as a mode of travel. In an effort to improve aviation communication, navigation, surveillance,

(CNS) and air traffic management (ATM) the International Civil Aviation Organisation (ICAO)

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developed standards for a future integrated system, this system was termed the Future Air

Navigation System (FANS) and would allow controllers to play a more passive monitoring role

through the use of increased automation and the wider application of RNAV operations with

increased reliance on satellite based navigation.

Today the world's Air Traffic Control (ATC) system still uses components defined in the 1940s

following the 1944 meeting in Chicago which launched the creation of the ICAO. This

traditional ATC system uses analogue radio systems for aircraft Communications, Navigation

& Surveillance (CNS). In 1983, THE ICAO established the special committee on the Future

Air Navigation System (FANS), charged with developing the operational concepts for the

future of Air Traffic Management (ATM). The FANS report was published in 1988 and laid the

basis for the industry's future strategy for ATM through digital CNS using satellites and data

links. Work then started on the development of the technical standards needed to realise the

FANS Concept.

In the early 1990s, the Boeing Company announced a first generation FANS product known

as FANS-1. Prior to this the international ATC system was not designed to fully take

advantage of flight deck capabilities. The FANS-1 package was based on the early ICAO

technical work for Automatic Dependent Surveillance (ADS) and Controller Pilot Data Link

Communications (CPDLC), and implemented as a software package on the Flight

Management Computer (FMS) of the Boeing 747-400. It used existing satellite based Aircraft

Communications Addressing and Reporting System (ACARS) communications (via Inmarsat

Data-2 service) and was targeted at operations in the South Pacific Oceanic region. The

deployment of FANS-1 was originally justified by improving route choice and thereby reducing

fuel burn.

The Data link Control and Display Unit (DCDU) on an Airbus A330,

the pilot interface for sending and receiving CPDLC messages.

A product similar to the FANS-1 package was later developed by Airbus for the A-340 and A-

330 and was known as the FANS-A package. Boeing also extended the range of aircraft

supported to include the Boeing 777 and 767. Together, the two products are collectively

known as FANS-1/A. The main industry standards describing the operation of the FANS-1/A

products are ARINC 622 and EUROCAE ED-100/RTCA DO-258. Both the new Airbus A-380

and Boeing 787 have FANS-1/A capability. The ICAO work continued after FANS-1 was

announced, and continued to develop the CNS/ATM concepts and now we are moving forward

again with the introduction of Performance-Based Navigation (PBN).

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1.2 Aircraft Area Navigation (RNAV) Computer System – Function

Today one may choose from a variety of different types of RNAV equipment, covering a wide range of

capability and sophistication. The term flight management systems (FMS) is often used to describe

any system which provides some kind of advisory or direct control capability for navigation (lateral

and/or vertical), fuel management, route planning, etc. Systems which are described as performance

management systems, fuel management systems, flight management control systems and navigation

management systems are also available. Throughout this document, FMS is used in a generic sense

and is not intended to imply any one specific type of system.

Many new public transport and business/executive jet aircraft have a flight management system

installation as an integral part of the avionics system, but many older aircraft have been retro-fitted

with FMS systems. The core of the FMS is a computer that, as far as lateral navigation is concerned,

operates with a large data base which enables many routes to be pre-programmed and fed into the

system. In operation, the system is constantly updated with respect to positional accuracy by

reference to conventional navigation aids, and the sophisticated data base will ensure that the most

appropriate aids are selected and tuned in to automatically.

A RNAV system can be viewed as a computer which creates an electronic ‗model‘ of the world and

then calculates and expresses the aircraft‘s position on this ‗model‘ world. In order to accurately place

or locate the aircraft‘s position on this world model, the RNAV system automatically accepts inputs

from various sources. These can be ground-based, satellite or airborne navigation aids or systems

e.g. VOR, DME, INS or GNSS. 3D position information can be obtained by, for example, use of four

or more satellites. Importantly, the quality of the available NAVAID infrastructure directly impacts the

accuracy of the navigation solution. Thus a patchy NAVAID environment might result in inconsistent

navigation accuracy. The ‗challenge‘ to achieving accurate, reliable, efficient and continued RNAV is

the accurate placement of the aircraft on its world model using the available NAVAID infrastructure.

However, the high quality of navigation based on RNAV is currently demonstrated world-wide by the

large number of aircraft operating using RNAV on conventional routes.

As stated earlier, RNAV systems can accept a variety of navigation inputs and these are;

VOR/DME,

OMEGA/very low frequency (VLF) (no longer functioning),

LORAN-C (no longer functioning),

Inertial Navigation Systems (INS),

DME/DME; and

Global Navigation Satellite Systems (GNSS).

It is generally assumed that all of the above systems are either coupled or capable of being coupled

directly to the auto-flight system (autopilot). This facility may become a prerequisite of future RNAV

equipment.

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RNAV System Capabilities - The following system functions are the minimum required to conduct

basic RNAV operations:

Continuous indication of aircraft position relative to track to be displayed to the pilot flying on a

navigation display situated in his primary field of view. In addition where the minimum flight

crew is two pilots, indication of aircraft position relative to track to be displayed to the pilot not

flying on a navigation display situated in his primary field of view.

Display of distance and bearing to the active (To) waypoint.

Display of ground speed or time to the active (To) waypoint.

Navigation data storage.

Appropriate failure indication of the RNAV system, including the sensors.

Pilot interface of a Basic RNAV system using ONLY GNSS input

Although one may be able to effectively conduct RNAV operation with a system as stipulated above

the ICAO has identified additional functions that it recommends should also be included in RNAV

system capabilities. The ICAO recommends that the following system functions and equipment

characteristics to be included in RNAV system capability:

Autopilot and/or Flight

Director coupling.

Present position in terms of

latitude and longitude.

"Direct To" function.

Indication of navigation

accuracy (e.g. quality

factor).

Automatic channel selection

of radio navigation aids.

Navigation data base.

Automatic leg sequencing

and associated turn

anticipation.

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1.2.1 Navigation

The FNC computes data including aircraft position, velocity, track angle, vertical flight path

angle, drift angle, magnetic variation, barometric-corrected altitude, estimated time of arrival

and wind direction and magnitude. It may also perform automatic radio NAVAID tuning as well

as support manual tuning.

While navigation can be based upon a single navigation signal source (e.g. GNSS), most

systems today are multisensory RNAV systems. Such systems use a variety of navigation

sensors including GNSS, DME, VOR and IRS to compute the position and velocity of the

aircraft. While the implementation may vary, the system will typically base its calculations on

the most accurate positioning sensor available.

The RNAV system will confirm the validity of the individual sensor data and, in most systems,

will also confirm the consistency of the various sets of data before they are used. GNSS data

are usually subjected to rigorous integrity and accuracy checks prior to being accepted for

navigation position and velocity computation. DME and VOR data are typically subjected to a

series of ―reasonableness‖ checks prior to being accepted for FNC radio updating. This

difference in rigour is due to the capabilities and features designed into the navigation sensor

technology and equipment. For multi-sensor RNAV systems, if GNSS is not available for

calculating position/velocity, then the system may automatically select a lower priority update

mode such as DME/DME or VOR/DME. If these radio update modes are not available or have

been deselected, then the system may automatically revert to inertial coasting (i.e. navigation

with reference to INS information). For single-sensor systems, sensor failure may lead to a

dead reckoning mode of operation.

As the aircraft progresses along its flight path, if the RNAV system is using ground NAVAIDs,

it uses its current estimate of the aircraft's position and its internal database to automatically

tune the ground stations in order to obtain the most accurate radio position.

Lateral and vertical guidance is made available to the pilot either on the RNAV system display

itself or supplied to other display instruments. In many cases, the guidance is also supplied to

an automatic flight guidance system. In its most advanced form, this display consists of an

electronic map with an aircraft symbol, planned flight path, and ground facilities of interest,

such as NAVAIDs and airports.

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Area Navigation enables the aircraft to fly a path, or 'leg', between points, called 'waypoints',

which are not necessarily co-located with ground-based navigational aids. If a navigation data

base is included in the RNAV system capabilities then the data in the database is specific to

an Aircraft Operator's (AO's)

requirements. This data is taken from

the States‘ Aeronautical Information

Publications (AIPs) in the form of route

structures, operational procedures and

Navigation Aids (NAVAIDs). The

intended flight path is programmed into

the FNC (RNAV system) by the pilot

and this is achieved by selecting or

inputting a series of waypoints using

the RNAV Control Unit. The RNAV

system defines the required flight path

by linking the waypoints together. It

uses the database (if fitted) to call up

details of the waypoints to do this. With

no database the pilot must insert all

waypoint data.

The intended flight path is then

displayed to the pilot on a Navigation

Display (ND). Simple RNAV systems

will display the lateral deviation from

the required track. If a map display is

available the RNAV system will display

the intended flight path on this map

display. The aircraft‘s position is

calculated using navigation signal

inputs. These navigation signal inputs into the FNC (RNAV system) are received via on-board

navigation sensors from either ground-based (DME or VOR), space-based (GNSS) NAVAIDs

or from on-board inertial platforms (INS). The coordinates of ground-based NAVAIDs are

taken from the navigation database (if fitted). The accuracy and consistency of the aircraft's

ability to fly the desired path is subject to the aircraft capabilities and on-board functionalities.

1.2.2 Navigation Database

Not all RNAV systems have a navigation database. Where a RNAV system has a navigation

database, this data base will store all the uploaded waypoints, path terminators and

coordinates for all ground-based NAVAIDs as required by that particular Aircraft Operator

(AO). The uploading of this information is done in accordance with a comprehensive laid

down procedure. The ICAO requires each State to publish its ATS routes, NAVAID

information, aerodrome and related procedures in the AIP (all this information to be in

accordance with an agreed to survey process and standard, WGS-84 at the moment).

AOs employ third party companies known as 'data houses' to compile specific information

from each State to support the AOs individual requirement (this normally relates to the AOs

route structure and usual destinations). These data houses produce the datasets using the

States‘ AIP as the primary source of information. These data sets are then packaged and

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shipped in ARINC 424 format to the Original Equipment (RNAV system) Manufacturers

(OEMs). The OEMs are known as 'data packers' and they then code and then upload the

datasets into the appropriate (target) RNAV systems. The data bases are updated and

validated in accordance with

the ICAO AIRAC

cycle. There are several

manufacturers of RNAV

systems and the formats

used by these systems are

different. Furthermore, no

two AOs will require exactly

the same information. Some

AOs will create company

routes (a pre-defined series

of waypoints) to enable

quicker uploads of specific

routes.

If the data in the dataset is

incorrect, the data in the

database will be incorrect

and the pilot may not be

aware of this. Good

airmanship dictates that the

flight path extracted from the

database be checked for

accuracy and consistency

against the chart information

before and during operation.

When using a RNAV system

with a database, the pilot will

select the ―company route‖

or the waypoints defining the

flight planned route in turn

from the database to create a route in the FNC (RNAV system). The pilot is unable to change

the navigation data in the database. This is a system design characteristic built into the

system to avoid risk of data corruption in the uploaded dataset. Most RNAV systems available

today include the ability to access a navigation database containing the waypoints, routes,

speeds and altitudes for published instrument flight procedures.

For RNAV systems without a database, the pilot is required to manually insert the waypoints

(key in the coordinates of each waypoint required to define the route). Systems with this

functionality will be limited in the navigation specifications that the aircraft can meet.

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1.2.3 Flight Planning

The flight planning function creates and assembles the lateral and vertical flight plan used by

the guidance function. A key aspect of the flight plan is the specification of flight plan

waypoints using latitude and longitude, without reference to the location of any ground

navigation aids.

More advanced RNAV systems include a capability for performance management where

aerodynamic and propulsion models are used to compute vertical flight profiles matched to

the aircraft and able to satisfy the constraints imposed by air traffic control. A performance

management function can be complex, utilising fuel flow, total fuel, flap position, engine data

and limits, altitude, airspeed, Mach, temperature, vertical speed, progress along the flight plan

and pilot inputs.

RNAV systems routinely provide flight progress information for the waypoints en-route, for

terminal and approach procedures, and the origin and destination. The information includes

estimated time of arrival, and distance-to-go which are both useful in tactical and planning

coordination with ATC

Manual or automated notification of an aircraft‘s qualification to operate along an ATS route,

on a procedure or in a particular portion of airspace is provided to ATC via the Flight Plan.

Flight Plan procedures are addressed in Procedures for Air Navigation Services — Air Traffic

Management (PANS-ATM) (Doc 4444).

1.2.4 Guidance and Control

A RNAV system provides lateral guidance, and in many cases, vertical guidance as well. The

lateral guidance function compares the aircraft‘s position generated by the navigation function

with the desired lateral flight path and then generates steering commands used to fly the

aircraft along the desired path. Geodesic or great circle paths joining the flight plan waypoints,

typically known as ―legs‖, and circular transition arcs between these legs are calculated by the

RNAV system. The flight path error is computed by comparing the aircraft‘s present position

and direction with the reference path. Roll steering commands to track the reference path are

based upon the path error. These steering commands are output to a flight guidance system,

which either controls the aircraft directly or generates commands for the flight director. The

vertical guidance function, where included, is used to control the aircraft along the vertical

profile within constraints imposed by the flight plan. The outputs of the vertical guidance

function are typically pitch commands to a display and/or flight guidance system, and thrust or

speed commands to displays and/or an auto-thrust function.

The difference between the required (ATS defined) and defined (RNAV system) paths, and

especially the ability to ―follow‖ required (ATS Defined) fixed path turns, depend on but is not

limited to:

the accuracy of the initial AIP navigation data as supplied by the State,

the coding accuracy of the dataset by the data packers,

the accuracy and quality of the navigation signals inputs,

the accuracy of the on-board navigation sensors,

the capabilities, functionalities and processing methodology of the RNAV system,

and/or,

the manual/Flight Director/autopilot control accuracy of the aircraft.

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1.2.5 Display and System Control

Display and system controls provide the means for system initialisation, flight planning, path

deviations, progress monitoring, active guidance control and presentation of navigation data

for flight crew situational awareness.

Garmin 530

RNAV system using GNSS, VOR, DME

and ILS input.

Garmin 430 RNAV

system using GNSS, VOR, DME and ILS

input.

FMS

Primary Navigation Display

In complex RNAV systems control is via FMS key pad and in basic systems via the CDU.

1.2.6 Manual Radio Position Updating

In older RNAV systems the INS position is programmed in by a flight crew member, this takes

time and is vulnerable to input errors. This position update is normally done during or just

prior to engine start-up. The INS position may also require manual position updating by a

crew member and if so, this type of system is limited in its application.

1.2.7 Automatic Radio Position Updating

More modern systems will update the INS position automatically using aircraft position

entered into the FMS by the crew during FMS initialisation, by conventional NAVAIDs, GBAS

or GRAS.

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1.3 Area Navigation (RNAV) Operations

In South Africa RNAV operations have been successfully implemented for the en-route phase

of flight between the three major city pairs as well as between Johannesburg and the major

coastal cities. We are now at the start of the process to expand this RNAV application into the

TMAs and the PBN implementation project will be the vehicle that will enable this expansion.

1.3.1 RNAV Routes

Volume II of the PBN Manual addresses the different Navigation Specifications which are

suited to one or more phases of flight.

a. EN-ROUTE:

Oceanic/Remote Continental

Continental

b. TERMINAL AIRSPACE:

Arrival/Departures

Approach:

o standard (RNP APCH) with or without vertical guidance, which everyone can fly, or

o demanding (RNP AR APCH) requiring specific approval, functionality and training.

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1.3.2 RNAV Waypoint types

The ICAO definition of a Waypoint: ‗A specified geographical location used to define an area

navigation route or the flight path of an aircraft employing area navigation.

A waypoint is defined as a geographic coordinate (in WGS84) and is identified as follows;

by a five letter unique name code, e.g. BARNA, or

by a three letter unique name code if located with a ground-based NAVAID using the three

letter ICAO identifier for that station, e.g. OTR, or

by a alphanumeric name code if used in Terminal Airspace only, DF410.

There are several different ways aircraft will fly to, from and between waypoints. As far as

procedure execution is concerned, the RNAV system will fly procedures in a consistent

manner, regardless of phase of flight, i.e. en-route or terminal. What will be noteworthy is the

fact that different RNAV systems and aircraft types will fly the same procedure in a slightly

different manner. These differences are due to small variations in the individual RNAV

systems analogue as well as individual aircraft flight performances. The way in which an

aircraft will fly a particular RNAV SID or STAR depends on the ‗waypoint types‘ and ‗leg types‘

used to define the procedure. RNAV leg types will be discussed under paragraph 1.5 RNAV

and RNP Specific Functions. RNAV procedures are designed to define lateral, longitudinal

and vertical navigation and waypoints are used to indicate a change in direction (track), speed

and/or height. To indicate such a change one may use one of two types of waypoints, either a

fly-by or a fly-over waypoint. The fly-by waypoint is used more often and is most commonly

used in terminal RNAV procedures.

a. Fly by waypoint:

A waypoint demanding

turn anticipation requiring the

aircraft to start turning before it

actually reaches the waypoint

thus allowing tangential

interception of the next

segment of a route or

procedure without the aircraft

actually passing overhead (or

―through‖) the waypoint. The

amount of distance of turn

anticipation (DTA) is

dependent on aircraft speed

and angle of back applied in

the turn. All turns under Instrument Flight Rules (IFR) are executed as rate one turns (i.e. 3

per second) or 25 angle of bank, whichever is less bank. This means that at a higher speed

the turn will be initiated sooner (further from the waypoint) than at a lower speed where the

turn will be initiated later (closer to the waypoint). With a higher speed the turn radius will be

larger than that for the same turn at a lower speed. This potential difference in flight path

produced by aircraft at different speeds needs to be understood, particularly be approach

controllers.

http://pbnwbt.ecacnav.com/pbn_package_site/glossary.htm#wgs

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b. Fly over waypoint:

A waypoint at which the turn

towards the next segment of a

route or procedure is initiated.

The turn is only initiated once

that aircraft actually passes

overhead (or ―through‖) the

waypoint. The extent to which

the aircraft will ‗overshoot‘ the

initial part of the next leg is

again dependent on aircraft

speed and angle of back

applied in the turn. The

resultant track error may be

corrected in a number of ways

and this will depend on the ‗leg

type‘ of this leg. Remember all turns under IFR are executed as rate one turns or 25 angle of

bank, whichever is less bank.

1.4 Required Navigation Performance (RNP) – Specification

1.4.1 Functional Capabilities and Limitations

Functional Capabilities.

a. RNP System — Basic Functions.

A RNP system is a RNAV system whose functionalities support on-board performance

monitoring and alerting. Current specific requirements include:

capability to follow a desired ground track with reliability, repeatability and predictability,

including curved paths; and

where vertical profiles are included for vertical guidance, use of vertical angles or

specified altitude constraints to define a desired vertical path.

The performance monitoring and alerting capabilities may be provided in different forms

depending on the system installation, architecture and configurations, including:

display and indication of both the required and the estimated navigation system

performance;

monitoring of the system performance and alerting the crew when RNP requirements

are not met; and

cross track deviation displays scaled to RNP, in conjunction with separate monitoring

and alerting for navigation integrity.

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A RNP system utilises its navigation sensors, system architecture and modes of operation to

satisfy the RNP navigation specification requirements. It must perform the integrity and

reasonableness checks of the sensors and data, and may provide a means to deselect

specific types of navigation aids to prevent reversion to an inadequate sensor. RNP

requirements may limit the modes of operation of the aircraft, e.g. for low RNP, where flight

technical error is a significant factor, manual flight by the crew may not be allowed. Dual

system/sensor installations may also be required depending on the intended operation or

need.

b. RNAV and RNP Specific Functions.

Performance-based flight operations are based on the ability to assure reliable, repeatable

and predictable flight paths for improved capacity and efficiency in planned operations. The

implementation of performance-based flight operations requires not only the functions

traditionally provided by the RNAV system, but also may require specific functions to improve

procedures, and airspace and air traffic operations. The system capabilities for established

fixed radius paths, RNAV or RNP holding, and lateral offsets fall into this latter category.

i. Lateral Navigation (LNAV):

The primary sensors used for

Area Navigation (laterally) are as

follows:

(1) Ground-based:

VOR/VOR

(Bearing/Bearing):

requires 2 stations to

estimate a position,

however poor

accuracy means that

this is not used by

RNAV systems.

VOR/DME

(Bearing/Range):

The angular error from

the VOR limits the

maximum range for

some navigation

applications.

DME/DME

(Range/Range):

requires a minimum of

2 DMEs (plus

ambiguity resolution)

to estimate a position,

supports all navigation applications down to the Final Approach Fix (FAF).

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(2) Space -based:

GPS and possibly GLONASS (once it becomes fully operational again):

a 3D position solution is calculated by estimating the range from 4 satellites.

ii. Vertical Navigation (VNAV):

(although briefly mentioned here, VNAV will be discussed in more detail under All Weather

Operations, Sensor Specific RNAV Procedures, Para 3.3.3.a, page 114)

There are 2 systems identified to support vertical navigation:

Barometric Altimetry - BARO VNAV:

Barometric Altimetry provides readings based on atmospheric pressure

(temperature dependant). The approach path will become shallower in colder

temperatures and steeper in higher temperatures.

Geometric Altimetry:

Geometric Altimetry is provided by GNSS. However, vertical accuracy of raw GPS is

insufficient for aviation applications. Therefore, other systems have been developed

to overcome this.

c. RNAV System Limitations.

There are also potential disadvantages to using RNAV in the terminal area:

Controllers will need to provide services to both RNAV and non-RNAV aircraft within

the same airspace.

RNAV databases and equipment are not fully standardised, and there is no firm

guidance on how the information is processed by aircraft systems. Tracks may be

flown slightly differently due to equipment, pilot technique or airline policies. However,

these track differences should not be significant enough to appear as deviations from

the published procedure.

Initially, controllers may be uncertain of the expected aircraft behaviour during a

RNAV turn, which may result in unnecessary vectors.

A common factor in each case is that RNAV procedures in the terminal area are relatively

new. Over time the number of RNAV operations will increase. Good procedure design,

effective training, and experience with terminal RNAV will increase pilot and controller

confidence in RNAV procedures.

1.4.2 RNAV System Requirements in terms of Accuracy, Integrity and continuity

a. RNAV Accuracy.

The precision with which a RNAV procedure is flown depends on the navigation source and

on the aircraft onboard equipment and database. Even though a standard format exists (i.e.,

ARINC 424), the coding of a RNAV SID or STAR into a database (or the interpretation of that

coding) may vary slightly. Differences in the databases along with variations in aircraft

performance may result in slightly different tracks being flown by RNAV capable aircraft on

the same procedure. This will be most apparent during turns and where fly-over waypoints

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are used. Tracking of a defined path by a RNAV capable aircraft is as accurate as, or better

than, that of aircraft flying conventional routes. In fact RNAV is often used to fly conventional

en route and terminal procedures

PBN operations require (lateral)

accuracy, integrity, continuity,

and availability of aircraft

systems together with particular

RNAV computer functionalities

to meet specific requirements.

These requirements are defined

for a particular Navigation

Application in the associated

Navigation Specification.

The lateral track accuracy is

defined by:

the path that has been

defined by the RNAV

system,

the navigation sensor used to estimate the position, and

the ability of the pilot and system to fly the defined path.

If the pilot or system is unable to maintain the defined path, this is known as the Flight

Technical Error (FTE). The performance limits for the FTE are laid down by the ICAO for each

RNP Specification. Position estimation accuracy is related to the type of navigation sensor

used; each sensor has its own error value,

called the ‗Navigation Sensor Error‘ (NSE).

It is also linked to the ‗dilution of precision'

(DOP). DOP is dependent upon the

relative angle the signals subtend at the

aircraft (angle of cut) and can be

considered the uncertainty in position

estimation.

Some sensors are better suited to RNAV

(PBN) operations than others:

NDB: is not an input to RNAV systems.

VOR: at long range is the least accurate of

the ground-based NAVAIDs used in Area

Navigation, it is too inaccurate for the more

demanding lateral track accuracy

requirements.

DME: providing there are sufficient stations

with appropriate geometry, supports most

Navigation Applications up to a simple

approach the accuracy of a DME/DME

position estimation is too poor when the

DOP of the signals from a pair of stations subtend less than 30° and more than 150°.

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GNSS (GPS and possibly other constellations): has the least error, with augmentation

(integrity checking), provides a navigation solution for every Navigation Application. The

aircraft manufacturers and AOs decide which sensors are fitted to the aircraft.

b. Integrity.

Integrity is the degree of confidence that can be placed on the position estimation by the

RNAV system. For flight applications using RNP systems, failure to meet the integrity

requirement should result in an alert to the pilot. This is also true for some RNAV systems. All

RNAV Systems using GPS as primary

navigation signal input are also

designed to provide an alert in the

event of navigation signal input failure

and/or RAIM failure.

GPS does not have an

acceptable alerting system for

civil aviation.

To provide the required alert,

Airborne Based Augmentation

Systems (ABAS) is employed.

ABAS provides integrity monitoring

by:

Aircraft Autonomous Integrity

Monitoring (AAIM) links the GPS

receiver to other aircraft

systems, or

Receiver Autonomous Integrity

Monitoring (RAIM), which

compares a series of position

estimations within the GPS unit

using redundant (extra) satellite signals

TSO 129 receivers provide this functionality. All TSO 129 certified receivers are capable of

Fault Detection (FD).

AAIM: Integrity monitoring is provided on the flight deck by linking the GPS receiver with

either an Inertial system or a Barometric altimeter.

RAIM is the most common form of integrity monitoring. It is an algorithm integrated in the

GPS receiver which compares a series of position estimations for internal consistency.

All forms of GPS augmentation will be discussed under paragraph 2, GNSS.

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c. Availability and continuity.

To meet a specific navigation application

both the signals-in-space and the aircraft

systems must meet the required accuracy,

integrity and continuity for that operation.

PBN requires that an aircraft and its systems

should be able to perform for the whole of

the defined operation, as long as it was

operating correctly at the start of that

operation. Equally, the signals from the

NAVAIDs should also be available for the

required operation and once the particular

phase of flight has begun, continue to

function for the period of that operation. The

Service Provider will need to consider how to

meet the appropriate requirement for signal

availability and continuity. This is usually

achieved through redundancy (additional

capability to handle failures), or by the

requirement for the aircraft to carry additional

systems (for example, carriage of IRS/IRU).

The probability of failure and therefore being

unable to complete an operation must be

acceptably low.

d. On-board Performance Monitoring and Alerting.

Aircraft RNAV systems do not necessarily

provide the pilot with a warning when the

required lateral accuracy limits have been

exceeded. However, some RNAV systems

do have extra functionality to monitor the

navigation sensor error (NSE) and issue

alerts. Those RNAV systems with this extra

functionality (on-board monitoring and

alerting) are RNP capable. Some

navigation applications will require RNP

capable systems for their operations.

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1.5 RNAV and RNP Specific Functions

1.5.1 RNAV Leg types

RNAV leg types are used to describe the path before, after or between waypoints. During the

design phase of a RNAV SID or STAR the leg type for the each leg is defined by the

procedure designers. The leg type may be any one of number of leg types (―path

terminators‖) as formulated by Aeronautical Radio Incorporated (AIRINC) in accordance with

what is known as the AIRINC 424 Navigation Database Specification. The ‗leg type‘ is part of

the information that is used to define each RNAV procedure and is contained in the data

package that is used to ‗build‘ the navigation database.

Generally only a few of the available leg types are used in the design of RNAV procedures. A

two-letter code is used to describe the leg type (e.g., heading = V, course = C, track = T, etc.)

and the leg end point (e.g., an altitude = A, distance = D, fix = F etc.). Although not explicitly

depicted on charts, controllers and pilots can determine leg types (and thus the expected

aircraft behaviour) by reading the relevant RNAV procedure chart narrative and viewing the

graphic depiction. The most

common leg types used are;

A "track" is a magnetic

course between waypoints

that must be intercepted

and flown. This is the most

common leg type and is

coded as "TF." Here the

aircraft will "track" from

ALPHA to BRAVO by

intercepting the magnetic

course between the two

waypoints after correcting

the track error resulting

from the flying over ALPHA

(ALPHA being a flyover

waypoint).

A "course" is a magnetic

course to a waypoint that

must be intercepted and

flown. A "CF" leg differs

from a "TF" only in that it

does not have a beginning

waypoint.

"Direct" describes a direct

course from an aircraft's

position to a waypoint. A

"DF" leg allows an

immediate turn to a

waypoint without requiring

intercept of a particular

course. Here the aircraft will

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proceed "direct" to BRAVO after crossing the fly-over waypoint ALPHA.

A "heading" is a magnetic heading to be flown. Heading legs are subject to wind drift. A

"VA" leg is a heading to an altitude and a "VM" is a heading to a "manual termination."

The "VA" leg is often used as the first leg of a RNAV departure. The "VM" leg is most

often used to end a RNAV STAR on, for example, a downwind leg heading.

Below we see the combination of a VA, CF, and TF that has been used to create the initial

portion of a RNAV SID.

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1.5.2 Fixed Radius Paths

a. Radius to Fix (RF):

This functionality is only used for

Standard Instrument Departures

(SIDs) and Standard Arrival Routes

(STARs).

b. Fixed Radius Transitions:

These transitions are used for

other Air Traffic Services (ATS)

routes, usually at higher altitudes.

The Fixed Radius Transitions

(FRTs), used in the en-route

phase of flight, have two turn radii:

15 NM below FL 190,

22.5 NM above FL 200.

These values are defined in the

industry standard DO236B/ED75B

c. Leg:

It is desirable to define how an aircraft will fly between waypoints, especially for consistent

and predictable flight behaviour. The path between two waypoints is normally called a

‗leg‘. With ATS routes, the aircraft will fly the ‗leg‘ to the next waypoint in sequence,

performing a fly-by turn where capable. For consistent ground tracks in the turn, an FRT can

be used. With SIDs and STARs each 'leg' is associated with a 'Path Terminator', which

defines how the path will be flown and how the ‗leg‘ will be terminated.

These ‗Path Terminators‘ have been defined by industry in a standard called ARINC

424.

RF (Radius to Fix), used for SIDs and STARs, is an example of a 'leg' whose path is a

fixed radius turn terminating at the next fix (which is a waypoint).

Historically, the textual description of the SID or STAR in the States‘ AIPs was the legal

statement of that procedure. This has led to ambiguity for those creating aircraft databases.

These issues are discussed in the topic 'Airspace Design'.

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1.5.3 Holding Pattern

The RNAV system facilitates the holding pattern specification by allowing the definition of the

inbound course to the holding waypoint, turn direction and leg time or distance on the straight

segments, as well as the ability to plan the exit from the hold. For RNP systems, further

improvement in holding is available. These RNP improvements include fly-by entry into the

hold, minimising the necessary protected airspace on the non-holding side of the holding

pattern, consistent with the RNP limits provided. Where RNP holding is applied, a maximum

of RNP 1 is suggested since less stringent values adversely affect airspace usage and

design.

1.5.4 Offset Flight Path

RNAV systems may provide the capability for the flight crew to specify a lateral offset from a

defined route. Generally, lateral offsets can be specified in increments of 1 NM up to 20 NM.

When a lateral offset is activated in the RNAV system, the RNAV aircraft will depart the

defined route and typically intercept the offset at a 45⁰ or less angle. When the offset is

cancelled, the aircraft returns to the defined route in a similar manner. Such offsets can be

used both strategically, i.e. fixed offset for the length of the route, or tactically, i.e. temporarily.

Most RNAV systems discontinue offsets in the terminal area or at the beginning of an

approach procedure, at a RNAV hold, or during course changes of 90⁰s or greater. The

amount of variability in these types of RNAV operations should be considered as operational

implementation proceeds.

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2 GLOBAL NAVIGATION SATELLITE SYSTEMS (GNSS)

2.1 Description of the GNSS Concept

Global Navigation Satellite Systems (GNSS) is the standard generic term for satellite navigation

systems (―sat nav‖) that provide autonomous geo-spatial positioning with global coverage. GNSS

allows small electronic receivers to determine their location (longitude, latitude and altitude) to within a

few metres using time signals transmitted along a line-of-sight by radio from satellites. Receivers

calculate the precise time as well as position.

As of 2010, the United States NAVSTAR Global

Positioning System (GPS) is the only fully

operational GNSS. The Russian GLONASS is a

GNSS in the process of being restored to full

operation (21 of 24 are operational). The

European Union‘s Galileo positioning system is a

GNSS in initial deployment phase, scheduled to

be operational in 2013/2014. The People‘s

Republic of China has indicated it will expand its

regional Beidou navigation system into the global

Compass navigation system by 2015 – 2017.

GNSS navigation services (i.e. position and time

data) may be obtained using various

combinations of the following elements installed on the ground, on satellites and/or on-board aircraft:

Global Positioning System (GPS) that provides the standard positioning service (SPS);

Global Navigation Satellite System (GLONASS) that provides the Channel of Standard Accuracy

(CSA) navigation signal;

Aircraft GNSS receivers

GNSS Augmentation Systems;

Aircraft-based augmentation system (ABAS)

Satellite-based augmentation system (SBAS);

Ground-based augmentation system (GBAS);

Ground-based regional augmentation system (GRAS)

Note that the position information provided by the GNSS to the user

shall be expressed in terms of the World Geodetic System – 1984

(WGS-84) geodetic reference datum. If GNSS elements, other than

WGS-84 coordinates are employed, appropriate conversion

parameters are to be employed. The time data provided by the GNSS

to the user shall be expressed in a time scale that takes the Universal

Time Coordinated (UTC) as reference.

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The basic GNSS concept is shown in the graphic below, which illustrates the steps involved in using

GNSS to determine time and position then applying this information.

Basic GNSS Steps

Step 1 – Satellites: GNSS satellites orbit the Earth. The satellites know their orbit ephemerides (the

parameters that define their orbit) and the time very, very accurately. Ground-based control stations

adjust the satellites‘ ephemerides and time, when necessary.

Step 2 – Propagation: GNSS satellites regularly broadcast their ephemerides and time, as well as

their status. GNSS radio signals pass through layers of the atmosphere to the user equipment.

Step 3 – Reception: GNSS user equipment receives the signals from multiple GNSS satellites then,

for each satellite, recovers the information that was transmitted and determines the time of

propagation, i.e. the time it takes the signals to travel from the satellite to the receiver.

Step 4 – Computation: GNSS user equipment uses the recovered information to compute time and

position.

Step 5 – Application: GNSS user equipment utilises the position and time information in their

applications, for example, navigation, surveying or mapping.

GNSS satellite signals are quite complex. Describing these signals requires equally complex

terminology such as pseudo-random, correlation and code division multiple access (CDMA). To

explain these GNSS concepts, let us first discuss GPS satellite signals.

GPS was designed as a positioning system for the US Department of Defence to provide high-

accuracy position information for military applications. A lot of complexity was designed into the

system to make it impervious to jamming and interference. Although military and civilian components

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of GPS are separate, some of the technologies used in the military component have been applied to

the civilian component.

The frequency plans (plans that describe the frequency, amplitude and width of signals) for each

GNSS constellation are a little different. To illustrate GNSS concepts, however, the frequency and

signal scheme used by GPS (as shown in the graphic below) will be briefly discussed. Conceptually,

this is not much different than the frequency plan for cable or broadcast television channels.

GPS Frequency Plan

As shown in the graphic above, GPS satellites transmit information on the L1, L2 and L5 frequencies.

You may ask, ―How can all GPS satellites transmit on the same frequencies?‖ GPS works the way it

does because of the transmission scheme it uses, which is called CDMA. CDMA is a form of spread

spectrum. GPS satellite signals, although they are on the same frequency, are modulated by a unique

pseudo-random digital sequence or code. Each satellite uses a different pseudo-random code.

Pseudo-random means that the signal only appears random; in fact, it actually repeats after a period

of time. Receivers know the pseudo-random code for each satellite. This allows receivers to correlate

(synchronise) with the CDMA signal for a particular satellite. CDMA signals are at a very low level, but

through this code correlation, the receiver is able to recover the signals and the information they

contain.

To illustrate, consider listening to a person in a noise-filled room. Many conversations are taking

place, but each conversation is in a different language. You are able to understand the person

because you know the language that they are speaking. If you are multi-lingual, you will be able to

understand what other people are saying too. CDMA is similar to this.

GPS operates in a frequency band referred to as the L-band; a portion of the radio spectrum between

1 and 2 GHz. L-band was chosen for several reasons, including:

Simplification of antenna design. If the frequency had been much higher, user antennae may

have had to be a bit more complex.

Ionospheric delay is more significant at lower frequencies.

Except through a vacuum, the speed of light is lower at lower frequencies, as is evident by the

separation of the colours in light by a prism.

The coding scheme requires a high band-width, which was not available in every frequency band.

The frequency band was chosen to minimise the effect that weather has on GPS signal

propagation.

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GPS Navigation Message

The P(Y) code is for military use. It provides better interference rejection than the C/A code, which

makes military GPS more robust than civilian GPS. The L2 frequency transmits the P(Y) code and on

newer GPS satellites, it also transmits the C/A code (referred to as L2C), providing a second publicly

available code for civilian users.

While the GPS transmission scheme is complex, it was chosen for many good reasons:

GPS receivers can recover very weak signals using very small antennae. This keeps the receiver

cost low.

Multi-frequency operation allows for ionospheric compensation, since ionospheric delays vary

with frequency.

The GPS is resistant to jamming and interference.

Security. Signals accessed and used by military applications are not accessible by civilians.

Other global navigation satellites systems are conceptually similar to GPS, but there are slight

differences (will be discussed at a later stage).

Why does time play such an important role in GNSS? It is because the time it takes a GNSS signal to

travel from satellites to receivers is used to determine distances (ranges) to satellites. Accuracy is

required because radio waves travel at the speed of light. In one microsecond (a millionth of a

second), light travels 300 m. In a nanosecond (a billionth of a second), light travels 30 cm. Small

errors in time can therefore result in large errors in position.

How does GNSS positioning actually work? For each satellite being tracked, the receiver calculates

how long the satellite signal took to reach it, as follows:

Propagation time = Time signal reached receiver – Time signal left satellite

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Multiplying this propagation time by the speed of light gives the distance to the satellite. For each

satellite being tracked, the receiver now knows where the satellite was at the time of transmission

(because the satellite broadcasts its orbital ephemerides) and it has determined the distance to the

satellite when it was there. Using trilateration, a method of geometrically determining the position of

an object, in a manner similar to triangulation, the receiver calculates its position.

To help you understand trilateration, the

technique is described in two dimensions. The

receiver calculates its range to Satellite A.

As mentioned, it does this by determining the

amount of time it took for the signal from

Satellite A to arrive at the receiver, and

multiplying this by the speed of light. Satellite A

communicated its location (determined from

the satellite orbit ephemerides and time) to the

receiver, so the receiver knows it is somewhere

on a circle radius equal to the range and

centred at the location of Satellite A, as

illustrated in the graphic on the right. In three

dimensions, you would show ranges as

spheres, not circles, but the explanation will

continue by referring to circles.

Ranging to First Satellite

The receiver also determines its range to a second satellite, Satellite B. Now the receiver knows it is

at the intersection of two circles, at either Position 1 or 2 as shown in the graphic below.

Ranging to Second Satellite

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You may be tempted to conclude that ranging to a third satellite would be required to resolve your

location to Position 1 or Position 2. But one of the positions can most often be eliminated as not

feasible because, for example, it is in space or in the middle of the Earth. You might be tempted to

extended this illustration to three dimensions and suggest that only three ranges are needed for

positioning. But as have been discussed earlier, four ranges are necessary. Why is this?

Receiver clocks are not

nearly as accurate as the

clocks on board the satellites.

Most are based on quartz

crystals and are accurate to

only about 5 parts per million.

If you multiply this by the

speed of light, it will result in

an accuracy of ± 1 500

metres. When you determine

the range to two satellites,

your computed positions will

be out by an amount

proportional to the inaccuracy

in your receiver clock, as

illustrated in the graphic on

the right.

Position Error

You want to determine your actual position but, as shown in the previous graphic, the receiver time

inaccuracy causes range errors that result in position errors. The receiver knows there is an error; it

just does not know the size of the error. If you now compute the range to a third satellite, it will not

intersect the computed position as illustrated in the graphic below.

Detecting Position Error

Now let us discuss one of the ingenious techniques used in GNSS positioning. The receiver knows

that the reason the pseudo-ranges to the three satellites are not intersecting is because its clock is

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inaccurate. The receiver is programmed to advance or delay its clock until the pseudo-ranges to the

three satellites converge at a single point as illustrated in the graphic below.

Convergence

The incredible accuracy of the satellite clock has now been ―transferred‖ to the receiver clock,

eliminating the receiver clock error in the position determination. The receiver now has both accurate

position and a very, very accurate time. This presents opportunities for a broad range of application,

such as navigation in commercial aviation.

The technique discussed shows how, in a two-dimensional representation, receiver time inaccuracy

can be eliminated and position determined using ranges from three satellites. When you extend this

technique to three dimensions, you need to add a range to a fourth satellite. This is the reason why

line-of-sight to a minimum of four GNSS satellites is needed to determine position.

There are various errors that can affect the accuracy of standard GNSS pseudo-range determination,

i.e. the determination of the pseudo-range to a single satellite. These errors are shown in the table

below:

Table: GNSS Errors

Contributing Source Error Range

Satellite clocks ± 2 m

Orbit errors ± 2.5 m

Ionospheric delays ± 5 m

Tropospheric delays ± 0.5 m

Receiver noise ± 0.3 m

Multipath ± 1 m

The degree with which the above pseudo-range errors affect positioning accuracy depends largely on

the geometry of the satellites being used. Techniques for reducing these errors will be discussed at a

later stage.

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Once the receiver has determined its position and time, this information is passed to and used by the

user application, such as a flight management system.

Various GNSS Receivers

2.1.1 Almanac

The almanac consists of coarse orbit and status information for each satellite in the GNSS

constellation, an ionospheric model, and information to relate satellite-derived time to

Coordinated Universal Time (UTC). In order to fully comprehend the role of the almanac it is

necessary to first describe the radio signals (navigation message) sent by a satellite.

GNSS Navigation Message

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L1 transmits a navigation message, the coarse acquisition (C/A) code (freely available to the

public) and an encrypted precision (P) code, called the P(Y) code (restricted access). The

navigation message is a low bit rate message that includes the following information:

GPS date and time;

Satellite status and health. If the satellite is having problems or its orbit is being adjusted,

it will not be usable. When this happens, the satellite will transmit the ―out-of-service‖

message.

Satellite ephemeris data, which allows the receiver to calculate the satellite‘s position.

This information is accurate to many, many decimal places. Receivers can determine

exactly where the satellite was when it transmitted its time.

Almanac, which contains information and status for all GPS satellites, so receivers know

which satellites are available for tracking. On start-up, a receiver will recover this

―almanac‖. The almanac consists of coarse (rough) orbit and status information for each

satellite in the constellation.

Each satellite continuously broadcasts a data signal containing navigational information. The

information consists of a 50 Hs signal and contains data that include satellite orbits, clock

corrections and other system parameters (i.e. information about the status of the satellite).

The complete data signal consists of 37 500 bit and a transmission rate of 50 bit/second

means that 12.5 minutes are necessary to receive the complete signal. This time is required

by the receiver until the first determination of a position is possible, if no information about the

satellites is stored or the information is outdated.

The data signal is divided into 25 frames, each having a length of 1 500 bit (meaning an

interval of 30 seconds for transmission).

Structure of the GPS Data of One Frame

The 25 frames are divided into sub-frames (300 bit/6 sec), which are again divided into 10

words each (30 bit/0.6 sec). The first word of each sub-frame is the TLM (telemetry word); it

contains information about the age of the ephemeris data. The next word is the HOW (hand

over word), which is used by military receivers. The rest of the first sub-frame contains data

about status and accuracy of the transmitting satellite as well as clock correction data. The

second and third sub-frames contain ephemeris parameters. Sub-frames four and five contain

the so-called almanac data which include information about orbit parameters of all satellites,

their technical status and actual configuration, identification number, etc.

Every 30 seconds the most important data for the position determination are transmitted.

From the almanac data the receiver identifies the satellites that are likely to be received at the

actual position of the receiver. The receiver limits its search to those previously defined

satellites and hence this accelerates the position determination.

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As mentioned earlier, the data signal contains a correction parameter for the satellite‘s clocks.

Why is this necessary if the atomic clocks are absolutely precise? Each satellite carries

several atomic clocks and has very accurate time. However, the atomic clocks of the

individual satellites are not synchronised to the GPS reference time, but run independently of

each other (periodic adjustments are made to align the timing of these clocks). Therefore,

correction data for the clocks of each satellite are required. Furthermore, the GPS reference

time is different from the UTC time. UTC is synchronised with the rotation of the Earth by

means of leap seconds.

A typical reason why satellites are marked as defective is the necessity for an orbit correction.

In such a case the satellite is marked as defective, once the satellite is stabilised in its new

orbit, the defective marking is removed.

When ephemeris and almanac data are stored in the receiver, the ―age‖ of the data will

influence how long the receiver needs to calculate the first position determination. If the

receiver has not had any contact with the satellites for an extended period of time, the first

position determination will take longer. If the contact has only been interrupted for a short time

(e.g. the aircraft was on the hardstand for a quick turn-around), the position determination is

restarted instantly. Establishing GNSS position calculation using visible satellites with good

geometry is known as reacquisition (or reacquire).

If position and time are known and the almanac and ephemeris data are up-to-date, the

system is able to reacquire the satellites almost instantaneously; this is referred to as a hot

start. This is the case when the receiver is turned on at approximately the same position

where it was turned off and within 2 – 6 hours after the last position determination. In this

case a position fix can be obtained within approximately 15 seconds (this may happen during

a quick turn-around or a short stop).

If the almanac data are available and the time of the receiver is correct but the ephemeris

data are outdated, the reacquisition will take a bit longer and this is referred to as a warm

start. In this case it takes about 45 seconds to actualise the ephemeris data and obtain a

position fix. Ephemeris data are outdated when more than 2 – 6 hours have elapsed since the

last data reception from the satellites in view. The more new satellites have come into view

since the last position determination, the longer the warm start takes.

If neither ephemeris nor almanac data and the last position are known, the acquisition

process is started with no known information; this is referred to as a cold start. The first step

then is that all the almanac data have to be collected from the satellites; this procedure takes

up to 12.5 minutes. This happens when the receiver was switched off for several hours, was

stored without batteries or was moved approximately 300 km or more since the last position

fix.

In the last case no almanac data have to be collected, but as the ―wrong‖ satellites are in

view, the receiver has to screen all the satellite data until it finds the information for the

satellites that are in view. For many receivers, the duration of a cold start can be shortened

when the date and approximate position are entered manually.

2.1.2 GNSS Segments

The GNSS consists of three major components or ―segments‖: the space segment, the

control segment and the user segment. These are illustrated in the graphic below.

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GNSS Segments

a. Space Segment

The space segment is composed of the

GNSS satellites orbiting about 20 000 km

above the Earth. Each GNSS has its own

―constellation‖ of satellites, arranged in orbits

to provide the desired coverage as

illustrated in the graphic on the right.

GNSS Satellite Orbits

Each satellite in a GNSS constellation broadcasts a signal that identifies it and provides its

time, orbit and status. To illustrate, consider the following: You are in town and decide to

phone a friend for a visit. You call and reach your friend‘s answering service, so you leave a

message:

―This is Peter (identity). The time is 2:30 PM (time). I am at the northwest corner of 1st

Avenue and 2nd

Street and I am heading towards your place (orbit). I am okay, but I

am a bit thirsty (status).‖

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Your friend returns a couple of minutes later, listens to your message and ―processes‖ it, then

calls you back and suggest that you proceed via a slightly different route; effectively, your

friend has given you an ―orbit correction‖.

b. Control Segment

The control segment comprises a ground-based network of master control stations, data

uploading stations, and monitor stations; in the case of GPS for example, two master control

stations (one primary and one back-up), four data uploading stations and ten monitor stations,

located throughout the world.

In each GNSS, the master control station adjusts the satellites‘ orbit parameters and on-board

high-precision clocks when necessary to

maintain accuracy.

Monitor stations, usually installed over a

broad geographic area, monitor the

satellites‘ signals and status, and relay

this information to the master control

station. The master control station

analyses the signals then transmits orbit

and time corrections to the satellites

through data uploading stations.

GPS ground control station in Hawaii

c. User Segment

The user segment consists of equipment that

processes the received signals from the GNSS

satellites and uses them to derive an apply

location and time information. The equipment

ranges from hand-held receivers used by hikers,

to sophisticated, specialised receivers used for

high-end survey and mapping applications and

commercial aviation.

A Variety of Hand-held GPS Receivers

In general, GNSS receivers are composed of an antenna, tuned to the frequencies

transmitted by the satellites, receiver processors and a highly-stable clock (often a crystal

oscillator). GNSS receivers therefore convert the GNSS satellite signals into position, and

time estimates. Four satellites are required to compute the four dimensions of X, Y, S (GNSS

WGS 84 position is expressed in terms of three axis X, Y and S) and time. Some receivers

may also include a display for providing location and speed information to the user (speed

can only be calculated if the GNSS receiver has a built-in area navigation computer to

calculate speed). A receiver is often described by the number of channels it is capable of

monitoring simultaneously. Originally limited to four or five satellites, this has progressively

increased over the years so that today receivers typically have between 12 and 20 channels.

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2.2 System Accuracy, Integrity, Continuity and Availability

The current core constellations (i.e. GPS and GLONASS) have the capability to provide

accurate position and time information worldwide. The accuracy provided by these systems

meets aviation requirements for en-route through non-precision approach, but not the

requirements for precision approach. Augmentation systems are used to meet the four basic

GNSS navigation operational performance requirements: accuracy, integrity, continuity and

availability. Navigation systems should be evaluated against these four essential criteria

before being introduced.

Availability is the cornerstone of these specifications in that it denotes the availability of

accuracy with integrity and continuity. The level of service and operational restrictions that

could be imposed depends on the level of availability of that service.

2.2.1 Signal Performance Requirement

GNSS position accuracy is the difference between the calculated and actual position of the

aircraft. Ground-based systems such as VOR and ILS have relatively repeatable error

characteristics, and therefore their performance can be measured for a short period of time

(e.g. during flight calibration) and it is assumed that the system accuracy does not change

after the measurement. GNSS errors however can change over a period of hours due to

satellite geometry changes, the effects of the ionosphere and augmentation system design.

While errors can change quickly for core satellite constellations, satellite-based augmentation

system and ground-based augmentation system errors would change slowly over time.

Integrity is a measure of the trust which can be placed in the correctness of the information

supplied by the total system. Integrity includes the ability of the system to alert the user when

the system should not be used for the intended operation (or phase of flight). The necessary

level of integrity for each operation is established with respect to specific horizontal/lateral

(and for some approaches, vertical) alert limits. When the integrity estimates exceed these

limits, the pilot is alerted within the prescribed time period. The type of operation and the

phase of flight dictate the maximum allowable horizontal/lateral and vertical errors and the

maximum time to alert the pilot. These are shown in the table below:

Table: GNSS Integrity Alert Limits by Airspace

Operation: Oceanic

en-route

Continental en-

route Terminal

Non-

precision

approach

Approach procedure

with vertical guidance

(APV) Category I

APV-I APV-II

Horizontal &

Lateral alert

limit

7.4 km

(4 NM)

7.4 to 3.7 km

(4 to 2 NM)

1.85 km

(1 NM)

556 m

(0.3 NM)

40 m

(130 ft)

40 m

(130 ft)

40 m

(130 ft)

Vertical alert

limit N/A N/A N/A N/A

50 m

(164 ft)

20 m

(66 ft)

10 to 15 m

(33 to 50 ft)

Maximum

alert time 5 min 5 min 15 sec 10 sec 6 sec 6 sec 6 sec

Following an alert, the crew should either resume navigation using traditional navigation aids

(NAVAIDs) or comply with procedures linked to a GNSS-based level of service with less

stringent requirements. For example, if alert limits are exceeded for Category I precision

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approach, before the aircraft crosses the final approach fix, the crew could restrict descend to

a decision altitude associated with APV operation.

Continuity is the capability of the system to perform its function without unscheduled

interruptions during the intended operation. This is expressed as a probability. For example,

there should be a high probability that the service remains available throughout a full

instrument approach procedure. Continuity requirements vary from a lower value for low

traffic density en-route airspace to a higher value for areas with high traffic density and

airspace complexity, where a failure could affect a large number of aircraft. Where there is a

high degree of reliance on the system for navigation, mitigation against failure may be

achieved through the use of alternative (most often conventional) navigation means or

through the use of air traffic control surveillance (most often radar monitoring) and

intervention to ensure that separation is maintained.

For approach and landing operations, each aircraft can be considered individually. The results

of a disruption of service would normally relate only to the risks associated with a missed

approach. For non-precision, APV and Category I approaches, missed approach is

considered a normal operation, since it occurs whenever the aircraft descends to the

minimum altitude for the approach and the pilot is unable to continue with visual reference.

This is therefore an operational efficiency issue, not a safety issue.

The availability of a service is the portion of time during which the system is simultaneously

delivering the required accuracy, integrity and continuity. The availability of GNSS is

complicated by the movement of satellites relative to a coverage area and by the potentially

long time it takes to restore a satellite in the event of a failure. The level of availability for a

certain airspace at a certain time should be determined through design, analysis and

modelling, rather than through measurement. The availability specifications (i.e. signal-in-

space performance requirements) in the table below, present a range of values valid for all

phases of flight. When establishing the availability requirements for GNSS, the desired level

of service to be supported is considered. Availability should be directly proportional to the

reliance on a GNSS element used in support of a particular phase of flight.

Table: Signal-in-space Performance Requirements

Typical

Operation

Accuracy

Horizontal

95%

(Notes 1 and 3)

Accuracy

Vertical

95%

(Notes 1 and 3)

Integrity

(Note 2)

Time-to-

alert

(Note 3)

Continuity

(Note 4)

Availability

(Note 5)

En-route 3.7 km

(2.0 NM)

N/A 1 – 1 x 10-7/h 5 min 1 – 1 x 10

-4/h

to 1 – 1 x 10-8/h

0.99 to

0.99999

En-route,

Terminal

0.74 km

(0.4 NM)

N/A 1 – 1 x 10-7/h 15 sec 1 – 1 x 10

-4/h

to 1 – 1 x 10-8/h

0.99 to

0.99999

Initial approach,

Intermediate

approach,

Non-precision

approach (NPA),

Departure

220 m

(720 ft)

N/A 1 – 1 x 10-7/h 10 sec 1 – 1 x 10

-4/h

to 1 – 1 x 10-8/h

0.99 to

0.99999

Approach

operations with

vertical guidance

(APV-I)

16.0 m

(52 ft)

20 m

(66 ft)

1 – 2 x 10-7/h

in any

approach

10 sec 1 – 8 x 10-6/h per

15 sec

0.99 to

0.99999

Approach

operations with

vertical guidance

(APV-II)

16.0 m

(52 ft)

8 m

(26 ft)

1 – 2 x 10-7/h

in any

approach

6 sec 1 – 8 x 10-6/h per

15 sec

0.99 to

0.99999

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Category I

precision

approach

(Note 7)

16.0 m

(52 ft)

6.0 m to 4.0 m

(20 ft to 13 ft)

(Note 6)

1 – 2 x 10-7/h

in any

approach

6 sec 1 – 8 x 10-6/h per

15 sec

0.99 to

0.99999

Notes:

1. The 95th percentile values for GNSS position errors are those required for the intended operation at the lowest height

above threshold (HAT), if applicable. Detailed requirements are specified in Annex 10 Volume 1 Appendix B and

guidance material is given in Attachment D, 3.2.

2. The definition of the integrity requirement includes an alert limit against which the requirement can be assessed.

These alert limits are: A range of vertical limits for Category I precision approach relates to the range of vertical

accuracy requirements.

3. The accuracy and time-to-alert requirements include the nominal performance of a fault-free receiver.

4. Ranges of values are given for the continuity requirement for en-route, terminal, initial approach, NPA and departure

operations, as this requirement is dependent upon several factors including the intended operation, traffic density,

complexity of airspace and availability of alternative navigation aids. The lower value given is the minimum

requirement for areas with low traffic density and airspace complexity. The higher value given is appropriate for areas

with high traffic density and airspace complexity. Continuity requirements for APV and Category I operations apply to

the average risk (over time) of loss of service, normalised to a 15-second exposure time.

5. A range of values is given for the availability requirements as these requirements are dependent upon the operational

need which is based upon several factors including the frequency of operations, weather environments, the size and

duration of the outages, availability of alternate navigation aids, radar coverage, traffic density and reversionary

operational procedures. The lower values given are the minimum availabilities for which a system is considered to be

practical but are not adequate to replace non-GNSS navigation aids. For en-route navigation, the higher values given

are adequate for GNSS to be the only navigation aid provided in an area. For approach and departure, the higher

values given are based upon the availability requirements at airport with a large amount of traffic assuming that

operations to or from multiple runways are affected but reversionary operational procedures ensure the safety of the

operation.

6. A range of values is specified for Category I precision approach. The 4.0 m (13 ft) requirement is based upon ILS

specifications and represents a conservative derivation from these specifications.

7. GNSS performance requirements for Category II and III precision approach operations are under review and will be

included at a later date.

8. The terms APV-I and APV-II refer to two levels of GNSS approach and landing operations with vertical guidance

(APV) and these terms are not necessarily intended to be used operationally.

Traffic density, alternate NAVAIDs, primary/secondary surveillance coverage, potential

duration and geographic size of outages, flight and ATC procedures are considered when

setting availability specifications for airspace, especially if the decommissioning of traditional

NAVAIDs is being considered.

An availability prediction tool can determine the periods when GNSS will not support an

intended operation. If this tool is used in flight planning, then from an operational perspective,

there remains only a continuity risk associated with the failure of necessary system

components between the time the prediction is made and the time the operation is conducted.

Typical Operation Horizontal alert limit Vertical alert limit

En-route (oceanic/continental

low density

7.4 km (4 NM) N/A

En-route (continental) 3.7 km (2 NM) N/A

En-route, Terminal 1.85 km (1 NM) N/A

NPA 556 m (0.3 NM) N/A

APV-I 40 m (130 ft) 50 m (164 ft)

APV-II 40 m (130 ft) 20 m (66ft)

Category I precision approach 40 m (130 ft) 15 m to 10 m

(50 ft to 33 ft)

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2.3 Augmentation

The existing core satellite constellations alone

do not meet strict aviation requirements of

accuracy, integrity, continuity and availability.

They meet the operational requirements for

various phases of flight, the core satellite

constellations require augmentation in the form

of aircraft-based augmentation systems (ABAS),

satellite-based augmentation systems (SBAS)

and/or ground-based augmentation systems

(GBAS). ABAS for example, rely on avionics

processing techniques or avionics integration to

meet aviation requirements. The other two

augmentation use ground monitoring stations to

verify the validity of satellite signals and

calculate corrections to enhance accuracy.

EGNOS Augmentation Satellite

SBAS delivers this information via a geostationary Earth orbit satellite, while GBAS uses a VHF data

broadcast (VDB) from a ground station.

The table below shows the potential of ABAS, SBAS or GBAS to meet the navigation requirements for

a particular phase of flight. However, the use of a specific augmentation system or a combination of

augmentation systems for specific operations within specified airspace needs to be approved by the

Appropriate Authority. Under risk management principles, some operational limitations may be

applied to compensate for availability or continuity performance that is lower than the specified levels.

Table: Level of Service from GNSS Augmentation Elements

Augmentation

element/operation

Oceanic

en-route

Continental

en-route Terminal

Instrument

approach and

landing*

Core satellite

constellation with ABAS

Suitable for

navigation when fault

detection and

exclusion (FDE) is

available.

Pre-flight FDE

predictions might be

required

Suitable for navigation

when receiver

autonomous integrity

monitoring (RAIM) or

another navigation

source is usable.

Suitable for

navigation when

RAIM or another

navigation source is

usable.

Suitable for non-

precision approach

(NPA) when RAIM is

available and another

navigation source is

usable at the alternate

aerodrome.

Core satellite

constellation with SBAS

Suitable for

navigation.

Suitable for

navigation.

Suitable for

navigation.

Suitable for NPA and

APV, depending on

SBAS performance.

Core satellite

constellation with GBAS

N/A GBAS positioning

service output may be

used as an input

source for approved

navigation systems.

GBAS positioning

service output may

be used as an input

source for approved

navigation systems.

Suitable for NPA and

precision approach

(PA) Category I

(potentially Category II

and Category III.

* Specific aerodrome infrastructure elements and physical characteristics are required to support the visual segment of

the instrument approach. These are defined in Annex 14 – Aerodromes and Aerodrome Design Manual (Doc 9157).

Various techniques have been developed (and are used by the augmentation systems) for extending

and improving the achievable accuracy. These techniques include dilution of precision; differential

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GNSS; carrier-based techniques and inertial navigation systems (these will be discussed at a later

stage).

2.3.1 Ground-Based Augmentation System (GBAS)

GBAS is a system for the augmentation of the accuracy, integrity, continuity and availability of

the information for navigation using GNSS. The GBAS ground sub-systems are Range

Reference stations (RRS); VHF data broadcast stations (VDB), Integrity monitoring stations

(IMS) and Processing base stations (PBS), integrated to execute the following main functions:

Provide locally relevant pseudo-range corrections;

Provide GBAS-related data;

Provide Final Approach Segment (FAS) data when supporting precision approach;

Provide predicted ranging source availability data; and

Provide monitoring of integrity for GNSS ranging sources.

The RRS receives the signals from the satellites that are in-view and provides pseudo-ranges

for the PBS. The PBS processes data and calculates the pseudo-range errors, including the

ranging sources availability, GBAS-related, final approach segment and atmospheric effects

data, and prepares the digital messages to be sent to the aircraft through the VDB.

The IMS monitors the operational state and the integrity of the GBAS ground sub-system

elements, as well as, the messages content, signals emitted by the VDB and quality of the

obtained pseudo-range errors. Another IMS function is to avoid that messages containing

misleading information be sent to the aircraft. The VDB broadcasts the GBAS messages to

aircraft operating inside its coverage.

GBAS is intended to support all types of approach, landing, take-off and surface operations

and may support en-route and terminal operations. The supported services are:

Category I precision approach;

Approach with vertical guidance; and

GBAS positioning information.

Probably the most well-known GBAS is the US developed Local Area Augmentation System

(LAAS), which is an all-weather aircraft landing system based on real-time differential

correction of the GPS signal. Local reference receivers, located around the airport, send data

to a central location at the airport. This data is used to formulate a correction message, which

is then transmitted to users via a VHF data link. A receiver on-board the aircraft uses this

information to correct GPS signals, which then provide a standard ILS-style display to use

while flying a precision approach.

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LAAS Architecture

2.3.2 Aircraft-Based Augmentation System (ABAS)

The core satellite constellations were not developed to satisfy the strict requirements for IFR

navigation. For this reason, GNSS avionics used in IFR operations should augment the

GNSS signal to ensure, amongst other things, its integrity. ABAS augments and/or integrates

GNSS information with information available on-board the aircraft to enhance the

performance of the core satellite constellations.

ABAS requires the use of one of the following techniques to enhance the performance

(accuracy, integrity, continuity and/or availability) of unaugmented GNSS and/or of the aircraft

navigation system:

Receiver Autonomous Integrity Monitoring (RAIM), which compares a series of position

estimations within the GPS unit using redundant (extra) satellite signals; or

Aircraft Autonomous Integrity Monitoring (AAIM), which links the GPS receiver to other

aircraft systems. Integrity monitoring is provided on the flight deck by linking the GPS

receiver with either an Inertial system or a Barometric altimeter.

a. Aircraft Autonomous Integrity Monitoring (AAIM).

AAIM uses the redundancy of position estimates from multiple sensors, including INS,

conventional NAVAIDs and/or GNSS, to provide integrity performance monitoring that is at

least equivalent to RAIM. This may be achieved by the use of INS or conventional navigation

sensors as an integrity check on GNSS data when RAIM is unavailable but GPS positioning

information continues to be valid.

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Non-GNSS information can be combined with GNSS information to enhance the performance

of the RNAV system. Examples include:

Using INS or Conventional NAVAIDs as the position inputs to ―coast‖ through short

periods of poor satellite geometry or when the aircraft structure shadows the GNSS

antennae while manoeuvring; and

Using GNSS sensor data as an input to a multi-sensor navigation solution calculated by

a RNAV system. This augmentation improves the availability of the aircraft‘s navigation

function.

b. Receiver Autonomous Integrity Monitoring (RAIM)

The most common ABAS technique is called RAIM. As mentioned above, RAIM requires

redundant satellite range measurements to detect faulty signals and alert the pilot. The

requirement for redundant signals means that navigation guidance with integrity, provided by

RAIM, may not be available 100% of the time. RAIM requirements may vary depending on the

type of operation; the requirements are lower for a non-precision approach than for terminal

applications, and are lower for terminal use than for en-route. It is for this reason that

GPS/RAIM approvals usually have operational restrictions.

RAIM algorithms require a minimum of five satellites in order to perform fault detection and

detect the presence of an unacceptably large position error for a given mode of flight. FDE

uses a minimum of six satellites not only to detect a faulty satellite but also to exclude it from

the navigation solution so that the navigation function can continue without interruption.

There are two distinct events that can cause a RAIM alert. The first is when there are not

enough satellites with adequate geometry in view. The position estimate may still be accurate,

but the integrity function of the receiver, i.e. the ability to detect a failed satellite, is lost. The

second is when the receiver detects a satellite fault and excludes this satellite from the

position calculation process (FDE). This type of alert results in the loss of the capability to

navigate based on GNSS position information. If either alert is experienced whilst on

approach, the pilot may no longer rely on GNSS position information for the purpose of

navigation during the remainder of the approach.

A barometric altimeter may be used as an additional measurement so that the number of

ranging sources required for RAIM and FDE can be reduced by one. Baro-aiding can also

help to increase availability when there are enough visible satellites, but their geometry is not

adequate to perform integrity function.

2.3.3 Space-Based Augmentation System (SBAS)

For applications where the cost of a differential GNSS augmentation system is not justified, or

if rover stations are spread over too large an area, spaced-based (or satellite-based)

augmentation systems (SBAS) may be more appropriate for enhancing position accuracy.

SBAS uses geosynchronous satellite systems that provide services for improving the

accuracy, integrity, and availability of GNSS signals.

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Accuracy is enhanced through the transmission of wide-area corrections for GNSS

range errors.

Integrity is enhanced by the SBAS network quickly detecting satellite signal errors and

sending alerts to receivers that they should not track the failed satellite.

Signal availability can be improved if the SBAS transmits ranging signals from its

satellites.

SBAS include reference stations, master stations, up-link stations and geosynchronous

satellites as illustrated in the graphic below. Reference stations, which are geographically

distributed throughout the SBAS service area, receive GNSS signals and forward them to the

master station. Since the locations of the reference stations are accurately known, the master

station can accurately calculate wide-area corrections.

SBAS – GNSS Data Gathering

As shown in the graphics below, corrections are up-linked to the SBAS satellite (left), then

broadcast to GNSS receivers throughout the SBAS coverage area (right).

SBAS – Correction Calculation and Up-link SBAS – Correction Broadcast

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User equipment receives the corrections and applies them to range calculations. SBAS

services can be grouped into two categories: free SBAS services and commercial SBAS

services. In general, free government-provided SBAS services use the same frequency as

GPS (CDGPS is an exception), and commercial SBAS services (such as OmniSTAR and

StarFire systems) use a different frequency. In this case additional equipment may be

required.

The following section provides a brief overview of some of the free SBAS services that have

been implemented around the world or are planned:

Wide Area Augmentation System (WAAS) has been developed by the US Federal Aviation

Administration (FAA) to provide GPS corrections and a certified level of integrity to the

aviation industry, to enable aircraft to conduct varying levels of precision approach to airports.

The corrections are also available free of charge to civilian users in North America. The Wide

Area Master Station (WMS) receives GPS data from Wide Area Reference Stations (WRS)

located throughout the USA. The WMS calculates differential corrections, then up-link these

to two WAAS geostationary satellites for broadcast across the USA as shown in the WAAS

architecture graphic below.

Separate corrections are calculated for

ionospheric delay, satellite timing and

satellite orbits; this allows error

corrections to be processed separately,

if appropriate, by the user application.

WAAS broadcasts correction data on

the same frequency as GPS, which

allows for the use of the same receiver

and antenna equipment as that used for

GPS. To receive correction data, user

equipment must have line-of-sight to

one of the WAAS satellites.

GPS Receiver display with WAAS

Wide Area Augmentation System (WAAS) Architecture

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The European Space Agency, in co-operation with the European Commission (EC) and Euro-

Control (European Organisation for the Safety of Air Navigation) has developed the

European Geostationary Navigation Overlay System (EGNOS), a regional augmentation

system that improves the accuracy of positions derived from GPS signals and alerts users

about reliability of the GPS signals.

The EGNOS satellites cover the European Union member nations and several other countries

in Europe. EGNOS is expected to be certified for safety-of-life applications in 2010. It

transmits differential correction data for public use. EGNOS satellites have also been placed

over the eastern Atlantic Ocean, the Indian Ocean, and the African mid-continent.

EGNOS Architecture

In Japan, the MTSAT satellite-based augmentation system (MSAS) has been developed

by the Japan Civil Aviation Bureau (JCAB). Successful launches of MTSAT-1R and MTSAT-2

were followed by integration of the MSAS ground system with the MTSATs by transmitting

test signals from MTSATs. The

purpose of these test signal

transmissions were to optimise

system performance and then to

verify that augmentation information

meets safety and performance

requirements. Since those tests had

been accomplished successfully,

MSAS for aviation use was

commissioned in September 2007.

MSAS Architecture

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In India, the Indian Space Research Organisation

(ISRO) and Airports Authority of India have

successfully completed the final system

acceptance test of the GPS Aided GEO

Augmented Navigation System (GAGAN).

With completion of the final system acceptance

test, the stage is set for India to embark on the next

phase of the programme, which will expand the

existing ground network, add redundancy, and

produce the certified analysis and documentation

for safety-of-flight commissioning.

Proposed GAGAN constellation

China is also planning SNAS (Satellite Navigation Augmentation System), to provide

WAAS-like service for the China-region.

The graphic below depicts the current world SBAS coverage. This graphic is only an

approximation of signal coverage by each of the SBAS constellations. Although there is

geographic coverage at higher latitudes, practical usage of SBAS will be limited to

environments where a relatively consistent line-of-sight to the satellites is available.

SBAS Global Footprint

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2.3.4 Ground-Based Regional Augmentation (GRAS)

GRAS is a blending of SBAS/GBAS concepts intended to enhance GPS/GNSS capabilities

for supporting civilian navigation needs. This approach is SBAS-like in its use of a distributed

network of reference stations for monitoring GPS and a central processing facility for

computing GPS integrity and differential correction information. But instead of transmitting this

information to users via dedicated Geostationary Earth Orbit (GEO) satellites, GRAS delivers

SBAS message data to a network of terrestrial stations for a local check as well as for

reformatting and rebroadcasting in the GBAS format in the 108 – 117.975 MHz band.

Each terrestrial station emits a GBAS-like VHF data

broadcast (VDB) signal in a managed time slot. Users can

employ a GPS/GRAS-capable receiver to obtain GPS

augmentation data for both continental en-route as well as

terminal approach/departure operations, depending on the

VHF network coverage. The GRAS approach could be

beneficial where a GEO satellite is either not available or

too costly to broadcast SBAS data. GRAS also allows for

national control of the system while providing unified

corrections and integrity for en-route capability.

VHF Data Broadcast Antenna

2.3.5 Techniques to improve GNSS receiver performance

As mentioned previously, various techniques have been developed to extend the accuracy of

GNSS receivers.

A commonly used technique for

improving GNSS performance

is differential GNSS, which is

illustrated in the graphic below.

Differential GNSS

Using differential GNSS, the position of a fixed GNSS receiver, referred to as the ―base

station‖ is determined to a high degree of accuracy using conventional surveying techniques.

The base station determines ranges to GNSS satellites in view by utilising two methods:

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Using the code-based positioning technique described earlier; or

Using the (precisely) known locations of the base station and the satellites, the location

of the satellites being determined from the precisely known orbit ephemerides and

satellite time.

The base station compares the ranges. Differences between the ranges can be attributed to

satellite ephemeris and clock errors, but mostly to errors associated with atmospheric delays.

Base stations send these errors to other receivers (rovers), which incorporate the corrections

into their position calculations.

Differential positioning requires a data link between base stations and rovers if corrections

need to be applied in real-time, and at least four GNSS satellites in view at both the base

station and the rovers. The absolute accuracy of the rover‘s computed position will depend on

the absolute accuracy of the base station‘s position.

Since GNSS satellites orbit high above the Earth, the propagation paths from the satellites to

the base stations and rovers pass through similar atmospheric conditions, as long as the base

station and rovers are not too far apart. Differential GNSS works very well with base-station-

to-rover separation of up to tens of kilometres, typically as used by LAAS.

The technique referred to as code-based positioning, is where the receiver correlates with

and uses the pseudo-random codes transmitted by four or more satellites to determine the

ranges to the satellites. From these ranges and knowing where the satellites are, the receiver

can establish its position to within a few metres. For applications such as aviation and

surveying, higher accuracies are required. Real-Time Kinematic (RTK), a technique that

uses carrier-based ranging, provides ranges (and therefore positions) that are orders of

magnitude more precise than those available through code-based positioning.

RTK techniques are complicated. The basic concept is to reduce and remove errors common

to a base station and rover pair, as illustrated in the graphic below.

Real-Time Kinematic

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At a very basic conceptual level, as shown in the graphic above, the range is calculated by

determining the number of cycles between the satellite and the rover station, then multiplying

this number by the carrier wave length.

The calculated ranges still include errors from such sources as satellite clock and

ephemerides, and ionospheric and tropospheric delays. To eliminate these errors and to take

advantage of the precision of carrier-based measurements, RTK performance requires

measurements to be transmitted from the base station to the rover station. A complicated

process called ―ambiguity resolution‖ is needed to determine the number of whole cycles.

Rovers determine their position using algorithms that incorporate ambiguity resolution and

differential correction. Like DGNSS, the position accuracy achievable by the rover depends

on, amongst other things, its distance from the base station (referred to as the ―baseline‖) and

the accuracy of the differential corrections. Corrections are as accurate as the known location

of the base station and the quality of the base station‘s satellite observations. Site selection is

important for minimising environmental effects such as interference and multipath, as is the

quality of the base station and rover receivers and antennae.

The geometric arrangement of satellites, as they are presented to the receiver, affects the

accuracy of position and time calculations. Receivers will ideally be designed to use signals

from available satellites in a manner that minimises this so called ―dilution of precision‖

(DOP).

To illustrate DOP, consider the example shown in the graphic below left, where the satellites

being tracked are clustered in a small region of the sky. In this example, intentionally a bit

extreme to illustrate the effect of DOP, it is difficult to determine where the ranges intersect.

Position is ―spread‖ over the area of range intersections, an area which is enlarged by range

inaccuracies (which can be viewed as a ―thickening‖ of the range line). As shown in the

graphic on the right, the addition of a range measurement to a satellite that is angularly

separated from the cluster allows you to determine a fix more precisely.

DOP (poor satellite geometry) DOP (improved satellite geometry)

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Although it is calculated using complex statistical methods, the following can be said about

DOP:

DOP is a numerical representation of satellite geometry, and it is dependent on the

locations of satellites that are visible to the receiver.

The smaller the value of DOP, the more precise the result of the time or position

calculation. The relationship is shown in the following formula:

Inaccuracy of Position Measurement = DOP x Inaccuracy of Range

Measurement

So, if DOP is very high, the inaccuracy of the position measurement will be much larger

than the inaccuracy of the range measurement.

DOP can be used as the basis for selecting the satellites on which the position solution

will be based; specifically, selecting satellites to minimise DOP for a particular

application.

A DOP above 6 results in generally unacceptable accuracies for DGPS and RTK

operations.

DOP varies with time of day and geographic location but, for a fixed position, the

geometric presentation of the satellites repeats every day, for GPS.

DOP can be calculated without determining the range. All that is needed is the satellite

positions and the approximate receiver location.

DOP can be expressed as a number of separate elements that define the dilution of precision

for a particular type of measurement, for example, HDOP (horizontal dilution of precision),

VDOP (vertical dilution of precision), and PDOP (position dilution of precision). These factors

are mathematically related. In some cases, for example when satellites are low in the sky,

HDOP is low and it will therefore be possible to get a good-to-excellent determination of

horizontal position (latitude and longitude), but VDOP may only be adequate for a moderate

altitude determination. Similarly, when satellites are clustered high in the sky, VDOP is better

than HDOP.

When we extend our DOP illustration to three

satellites, one way to view dilution of precision is to

consider the ―tetrahedron‖ formed by having the

satellites at three corners and the receiver at the

fourth, as illustrated graphically on the right.

Minimising DOP is not unlike maximising the volume

of this tetrahedron. When satellites are tightly

clustered and the angle between the satellites is

small, the tetrahedron is long and narrow. The

volume of the tetrahedron is small and DOP is

correspondingly high (undesirable). When the

satellites are located near the horizon, the

tetrahedron is flat. Again, the volume of the

tetrahedron is small and DOP is high. When the

satellites are not tightly clustered in the sky or low in

elevation, the volume of the tetrahedron approaches

a maximum and DOP is at its lowest (desirable).

Minimising DOP

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Northrop-Grumman LN-100R

Embedded INS/GPS

In Canada and other countries at high latitude, GNSS satellites are lower in the sky, and

achieving optimal DOP for some applications, particularly where good VDOP is required, is

sometimes a challenge.

When there were fewer GNSS satellites, achieving good DOP was sometimes difficult. These

difficulties are being reduced with more GNSS constellations and satellites coming on line

every year. Applications where the available satellites are low on the horizon or angularly

clustered may still expose the user to the pitfalls of

DOP. If you know your application will have

obstructed conditions, you may want to use a mission

planning tool in assist in your flight planning.

As discussed, GNSS use signals from orbiting

satellites to compute position, time and velocity.

GNSS navigation has excellent accuracy provided

the antenna has good visibility to the satellites. When

the line-of-sight to the satellites is blocked by

obstructions such as severe cloud cover, navigation

becomes unreliable or impossible. Inertial

Navigation System (INS) use rotation and

acceleration information from an Inertial

Measurement Unit (IMU) to compute accurate

position over time. An INS can also solve the attitude (roll, pitch and heading) of a vessel and

is not reliant on any external measurement to compute solution. In the absence of external

reference, however, the INS solution drifts over time due to accumulating errors in the IMU

data. When combined, the two techniques (GNSS and INS) enhance each other to provide a

powerful navigation solution.

The degree with which the GNSS and INS technologies are integrated varies with product

implementation. For example, in tightly coupled solutions, GNSS observations are used

directly by the inertial solution to take advantage of available GNSS data, even when only a

few satellites are visible (for instance, to reset or adjust the position being input by the INS).

Tightly coupled solutions allow feedback of the inertial solution into the GNSS receiver to

improve GNSS performance, for example, signal acquisition and convergence time. To

summarise, combining GNSS and INS technologies significantly increases opportunities for

application development by overcoming the limitations of the individual technologies.

2.3.6 GNSS Liability

In the development of GNSS, liability relating to signal accuracy and continuity is an issue that

is often raised; however, there is currently no satisfactory solution to this problem (see note

on the next page). Even in regulatory agencies there seems to be confusion about the status

of GNSS, but they accept the partial certification of GNSS products and related services. The

facts are that GNSS is in use in Civil Aviation today and aircraft are being supplied with

related installations and certified to ―near CAT I‖ levels. However, the use of GNSS in Public

Transport Operations still raises concern, largely because of the potential consequences of a

GNSS failure. Despite this, liability still appears relatively low on the agenda, since it is widely

assumed that these issues will be resolved when ―appropriate‖ institutional arrangements are

put in place by the ICAO. Yet, whether this is a realistic expectation seems very unclear.

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Note: — The liability issues regarding signal accuracy and continuity is currently addressed

through augmentation requirements. This is seen as the only effective means of

addressing this issue.

GNSS raises technical, commercial, political, military, institutional and legal issues. There are

many factors that must be taken into account in order to navigate through the potential

minefield that lies in the path of user airliner, airports, ATM providers, manufacturers and

individual States as they make strategic decisions that will affect their businesses in

generations to come.

Issues such as liability, certification, etc. are not just

purely altruistic considerations. GNSS is not a system

designed solely or specifically for civil aviation. GNSS

has many wide ranging applications across all

industry sectors and its applications are not just

limited to navigation. Indeed, no Civil Aviation

Authority or group of CAAs could muster even a tiny

fraction of the resources that are required to launch a

GNSS. The list of applications and the value of these

applications is so great, that the civil aviation market

is actually small by comparison, but still very large. This is one of the keys to the problem:

GNSS is a generic service of huge commercial significance.

The ICAO generally requires its members to accept the certification given by other States to

its own navigation services and that the ICAO members accept the certification given by a

member State to its registered aircraft and licensed crew.

The ICAO is setting standards for both GNSS and GNSS-based services. These standards

naturally assumed a GPS-like service. Thus the ICAO is essentially ―retro-fitting‖ standards to

an existing service (and assuming some upgrading of those services). Theoretically speaking,

the ICAO‘s role is simply to set safety and interoperability standards. In reality, the ICAO‘s

actual role in GNSS standardisation is a little anomalous, as it appears to be taking a lead (in

defining standards) when so many other sectors have a possibly greater interest. This is, in

part, based on the assumption that aviation is the most demanding user in safety.

Indeed, many have assumed that GNSS would somehow be ―approved‖ by the ICAO;

however, this UN Institution has no power or precedent for giving any approval that would be

legally effective. The ICAO is more a forum for agreeing common standards and settling

relations on civil aviation matters between its members. It is not an Agency with any

delegated power to carry out approvals; these are the sovereign responsibilities of the

member States. In reality, the ICAO concentrates on the interoperability of GNSS (to prevent

divergent satellite navigation systems) and the safety of augmentation systems (provided by

civil aviation).

However, legal liability has to be assured in some way to protect the interests of the civil

community in the event of a serious GNSS failure. Conversely, steps would also have to be

taken to protect a GNSS provider from hostile legal measures following a major accident or

disaster linked to its services.

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Legal arrangements should be made for GNSS service providers in order to limit or indemnify

it against loss or interruptions in service. If an accident were attributable to a GNSS failure,

then this may lead to modifications to GNSS or restrictions in its use. In order to provide the

necessary assurances required for GNSS operations, a certain level of service will have to be

―guaranteed‖ and this service level must then be bolstered by augmentation

systems.

The ICAO ensures interoperability between GNSS services and specifies

safety standards for augmentation systems for civil aviation applications.

Consequently, technical liability of GNSS cannot be effectively

traceable or enforceable; rather, the emphasis is on

augmentations systems, with certification remaining the

prerogative of a State.

2.4 Description of Receiver

The primary components of the GNSS user

segment are antennae and receivers, as shown

in the graphic on the right. Depending on the

application, antennae and receivers may be

physically separate or they may be integrated

into one assembly.

GNSS antennae receive the radio signals that

are transmitted by the GNSS satellites and send

these signals to the receivers.

GNSS User Equipment

GNSS antennae are available in a range of shapes, sizes and performances. The antenna is selected

based on the application. While a large antenna may be appropriate for a base station, a low-profile

aerodynamic antenna may be more suitable for aircraft installations.

Receivers process the satellite signals recovered by the antenna to calculate position and time.

Receivers may be designated to use signals from one GNSS constellation or from more than one

GNSS constellation. As with antennae, receivers may be packaged for a particular application, such

as aviation or agriculture.

However, as with any other item of

avionics equipment, a GNSS

receiver is required to be of an

approved type and to be installed

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in accordance with specific criteria. Any installation should be validated by a series of tests,

measurements (calibration) and inspections.

A typical GNSS receiver/display used in aviation

GNSS navigation equipment must have US FAA Technical Standard Order (TSO) C-129

authorisation. (See SA-CATS-91.05.1 Communication Equipment.)

2.4.1 Display

A GNSS avionics system may typically be an integrated, panel-mount, IFR navigation/

communication (NavComm) system. Although various products are available, they mostly

have the same basic display functions. When using a GNSS NavComm system for the first

time, it is recommended that the aircraft be moved to a location that is well clear of any

buildings and other aircraft so that the unit can collect satellite data without interruption.

The basic display and primary functions discussed in this section is that of the Garmin

GNS430. It is however important to note that the specific user manual for each NavComm

system be referred to prior

to using the system.

The key and knob

descriptions provide a

general overview of the

primary function(s) for each

key and knob. Data is

entered using the large and

small knobs.

Garmin GNS430

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Left-hand keys and knobs include:

The COM Power/Volume knob which controls unit power and communications radio

volume. Press momentarily to disable automatic squelch control.

The VLOC Volume knob which controls audio volume for the selected VOR/Localiser

frequency. Press momentarily to enable/disable the ident tone.

The large left knob (COM/VLOC) which is used to tune the megahertz (MHz) value of

the standby frequency for the communications transceiver (COM) or the VLOC receiver,

whichever is currently selected by the tuning cursor.

The small left knob (COM/VLOC) which is used to tune the kilohertz (KHz) value of the

standby frequency for the communications transceiver (COM) or the VLOC receiver,

whichever is currently selected by the tuning cursor. Press this knob momentarily to

toggle the tuning cursor between COM and VLOC frequency fields.

The COM flip-flop key which is used to swap the active and standby COM frequencies.

Press and hold to select emergency channel (121.500 MHz).

The VLOC flip-flop key which is used to swap the active and standby VLOC

frequencies (i.e., make the selected standby frequency active).

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The right-hand keys and knobs include:

The RNG key which allows the pilot to select the desired map range. Use the up arrow

to zoom out to a larger area, or the down arrow to zoom in to a smaller area.

The Direct-to key which provides access to the direct-to function that allows the pilot to

enter a destination waypoint and establishes a direct course to the selected destination.

The MENU key which displays a context-sensitive list of options. This options list allows

the pilot to access additional features or make settings changes which relate to the

currently displayed page.

The CLR key which is used to erase information, remove map detail, or to cancel an

entry. Press and hold the CLR key to immediately display the Default NAV page.

The ENT key which is used to approve an operation or complete data entry. It is also

used to confirm information, such as during power on.

The large right knob which is used to select between various page groups: NAV, WPT,

AUX or NRST. With the on-screen cursor enabled, the large right knob allows the pilot to

move the cursor about the page. The large right knob is also used to move the target

pointer right (turn clockwise) or left (counter-clockwise) when the map panning function

is active.

The small right knob which is used to select between the various pages within one of

the groups listed above. Press this knob momentarily to display the on-screen cursor.

The cursor allows the pilot to enter data and/or make a selection from a list of options.

When entering data, the small knob is used to select the desired letter or number and

the large knob is used to move to the next character space. The small right knob is also

used to move the target pointer up (turn clockwise) or down (counter-clockwise) when

the map panning function is active.

The bottom row keys include:

The CDI key that is used to toggle which navigation source (GPS or V/LOC) provides

output to an external HSI or CDI.

The OBS key which is used to select manual or automatic sequencing of waypoints.

Pressing the OBS key selects OBS mode, which retains the current ―active to‖ waypoint

as the navigation reference even after passing the waypoint (i.e., prevents sequencing to

the next waypoint). Pressing the OBS key again returns the unit to normal operation,

with automatic sequencing of waypoints. When OBS mode is selected, the pilot may set

the desired course to/from a waypoint using the ―Select OBS Course‖ pop-up window, or

an external OBS selector on the HSI or CDI.

The MSG key which is used to view system messages and to alert the pilot to important

warning and requirements.

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The FPL key which allows the pilot to create, edit, activate and invert flight plans, as well

as access approaches, departures and arrivals. A closets point to flight plan feature is

also available from the FPL key.

The PROC key which allows the pilot to select and remove approaches, departures and

arrivals from the flight plan. When using a flight plan, available procedures for the

departure and/or arrival airport are offered automatically. Alternatively the pilot may

select the desired airport, then the desired procedure.

The unit‘s display is divided into separate ―windows‖ (or screen areas), including a COM window,

VLOC window and a GPS window.

Unit display windows

2.4.2 Functionality

Although the functionality of GNSS receivers (especially when it is an integrated NavComm

system) is comprehensive, only the basic functions related to the satellite/receiver interaction

will be discussed. Once again the Garmin GNS430 will be used as an example.

The Satellite Status Page appears as the unit attempts to collect satellite information.

When an ―Acquiring‖ status is displayed on the Satellite Status page, the signal

strengths of any satellite received appear as ―bar graph‖ readings. This is a good

indication that the unit is receiving signals and a position fix is being determined.

Following the first-time use if the unit, the time required for a position fix varies, usually

from one to two minutes. If the unit can only obtain enough satellites for 2-D navigation

(i.e. no altitude), the unit uses the altitude provided by the altitude encoder (if one is

connected). The ―INTEG‖ annunciator (bottom left corner of the screen) indicates that

satellite coverage is insufficient to pass built-in integrity monitoring tests. In the example

graphic shown below, not enough satellites are being received to determine a position.

The Satellite Status page shows the ID numbers for the satellites and the relative signal

strength of each satellite received (as a ―bar graph‖ reading). ―Searching Sky‖ indicates

that satellite almanac data is not available or has expired (if the unit has not been used

for six months or more). This means the unit is acquiring satellite data to establish

almanac and satellite orbit information, which can take five to ten minutes. The data is

re-collected from the first available satellite. The Satellite Status Page displays a

―Search Sky‖ status, and the message annunciator (MSG), above the MSG key also

flashes to alert the pilot of system message, ―Searching the sky‖ (to view a system

message, press the MSG key).

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Satellite Status Page Message

Page

The Satellite Status Page also provides a visual reference of GPS receiver functions,

including current satellite coverage, GPS receiver status and position accuracy. This

page is also helpful in troubleshooting weak (or missing) signal levels due to poor

satellite coverage or installation problems.

Satellite Status Page Annotations

As the GPS receiver locks onto satellites, a signal bar appears for each satellite in view,

with the appropriate satellite number underneath each bar. The progress of satellite

acquisition is shown in three stages:

No signal strength bar – the receiver is looking for the satellites indicated;

Hollow signal strength bars – the receiver has found the satellite(s) and is collecting

data;

Solid signal strength bars – the receiver has collected the necessary data and the

satellite(s) is ready for use.

Chequered signal strength bars – Excluded satellites.

The sky view display (at top left corner of the page) shows which satellites are currently in

view, and where they are. The outer circle of the sky view represents the horizon (with north

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at top of the page); the inner circle 45° above the horizon; and the centre point directly

overhead.

Remember that each satellite has a 30-

second data transmission that must be

collected (hollow signal strength) before

the satellite may be used for navigation

(solid signal strength). Once the

receiver has determined the present

position the unit indicates position, track

and ground speed on the other

navigation pages.

Hollow signal strength bars

The Satellite Status Page also indicates the accuracy of the position fix using estimated

position error (EPE), dilution of precision (DOP) and horizontal uncertainty level (HUL)

figures. DOP measures satellite geometry quality (i.e., number of satellites received and

where they are relative to each other) on a scale from one to ten. The lowest numbers are the

best accuracy and the highest numbers are the worst. EPE uses DOP and other factors to

calculate a horizontal position error.

When so authorised, a GNSS receiver may provide non-precision approach guidance.

Some receivers may also be used as a supplemental aid for precision approaches, but if

not appropriately authorised, the localiser and glide slope receivers must be used for

primary approach course guidance. Approaches designed specifically for GNSS are

often very simple, and don‘t require overflying a VOR or NDB. Many non-precision

approaches have ―GPS overlays‖ to allow the pilot to fly an existing procedure (VOR,

VOR/DME, NDB, RNAV, etc.) more accurately using GNSS.

a. Fault Detection and Exclusion (FDE).

FDE consists of two distinct parts: fault detection and fault exclusion. Fault detection (RAIM)

detects the presence of an unacceptable large pseudo-range error (and presumably, position

error) for a given mode of flight or a satellite failure which can affect navigation. Fault

detection is synonymous with RAIM (Receiver Autonomous Integrity Monitoring). Upon

detection of a fault, fault exclusion follows and excludes the source of the unacceptable large

pseudo-range error, thereby allowing navigation to return to normal without an interruption in

service. FDE functionality is provided for oceanic, en-route, terminal and non-precision

approach phases of flight. The FDE functionality adheres to the missed alert probability, false

alert probability and failed exclusion probability specified by TSO-C145a/C146a.

FDE requires no pilot interaction during flight, but predicting the capability of the GNSS

constellation to provide service during a flight is done by the pilot prior to departure. FDE

prediction allows the pilot to specify the planned departure date/time, route type, ground

speed, ground speed variation and maximum allowable outage. When provided through

NOTAM or other sources, GNSS satellites with known failures can be excluded through the

prediction programme‘s setup function. On most GNSS receivers, the pilot can view the

information related to FDE operation.

The image below shows satellite number 9 exclusion during the oceanic phase of flight. In

addition to EPE and DOP, the HUL field displays a 99% confidence level that the aircraft

position is within a circle with a radius of the value (0.05 NM) displayed in the HUL field.

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Satellite Status Page

2.4.3 Integrity Alerts

As mentioned before, RAIM is the

technology developed to assess the

integrity of GNSS signals in a receiver

system. It is of special importance in a

safety-critical GNSS application, such

as aviation or marine navigation. RAIM

detects faults with redundant GNSS

pseudo-range measurements. That

means, when more satellites are

available than needed to produce a

position fix, the extra pseudo-ranges should all be consistent with the computed position. A

pseudo-range differing significantly from the expected value may indicate a fault with the

associated satellite (such as clock failure) or another signal integrity problem (such as

ionospheric dispersion).

The basic GNSS receiver has three modes of operation; en-route (oceanic), terminal and

approach mode. The RAIM alert limits are automatically coupled to the receiver modes are

set to 2.0 NM (±3.7 km), 1.0 NM (1.9 km) and 0.3 NM (0.6 km) respectively.

a. Constellation Alerts.

Ephemeris prediction errors are errors in the declared position of a satellite (as transmitted in

the navigation data message). In other words; the satellite wasn‘t where the system said it

was when you made a measurement on its signal. Radial and cross-track errors contribute to

ephemeris errors. Ephemeris corrections are calculated using a curve-fit of the control

segment‘s best prediction of each satellite‘s position at the time of an upload and contain

inherent errors. In addition, the errors tend to grow over time from the last control segment

navigation data upload. The constellation errors will be made visible to the user by FDE.

b. Receiver Related Alerts.

As mentioned before, there are a number of manufacturers of basic GNSS receivers on the

market and each employs a different method of interface. It is therefore advisable for flight

crews to become thoroughly familiar with the operation of their particular receiver prior to

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using it in flight operations. The equipment must be operated in accordance with the

provisions of the applicable aircraft operating manual. It is also advisable to have one of the

appropriate checklists available on-board the aircraft for easy reference in the sequential

loading and operation of the equipment.

The CDI sensitivity is automatically coupled to the operating mode of the receiver and is set to

5.0 NM (±9.3 km), 1.0 NM (1.9 km) or 0.3 NM (0.6 km) for en-route, terminal and approach

respectively. Although a manual selection for CDI sensitivity is available, overriding and

automatically selected CDI sensitivity during an approach will cancel approach mode.

Navigation display with CDI and Route Information

The failures caused by the GNSS receiver can have two consequences on navigation system

performance, which are the interruption of the information provided to the user or the output of

misleading information. Neither of these events is accounted for in the signal-in-space

requirement.

The nominal error of the GNSS aircraft element is determined by receiver noise, interference,

and multi-path and tropospheric model residual errors.

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2.5 NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System)

GPS was the first global navigation satellite system. GPS (or NAVSTAR,

as it is officially called) satellites were first launched in the late 1970‘s and

early 1980‘s for the US Department of Defence. Since then, several

generations (referred to as ―Blocks‖) of GPS satellites have been

launched. Initially, GPS was available only for military use but in 1983, a

decision was made to extend GPS to civilian use. The GPS constellation

is illustrated in the graphic below:

The NAVSTAR GPS Constellation

The GPS space segment is summarised in the table below. The orbit period of each satellite is

approximately 12 hours, so this provides a GPS receiver with at least six satellites in view from any

point on the Earth, under open-sky conditions.

Table: GPS Satellite Constellation

Satellites 21 plus 3 spare

Orbital planes 6

Orbit inclination 55⁰

Orbit radius 26 560 km

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A GPS satellite orbit is illustrated in the

graphic on the right.

GPS satellites continually broadcast

their identification, ranging signals,

satellite status and corrected

ephemerides (orbit parameters). The

satellites are identified either by their

Space Vehicle Number (SVN) or their

Pseudo-Random code Number (PRN).

GPS Satellite Orbit

The table below provides further information on GPS signals. GPS signals are based on CDMA (Code

Division Multiple Access) technology.

GPS Signal Characteristics

Designation Frequency Description

L1 1575.42 MHz

L1 is modulated by the C/A code (Coarse/Acquisition) and the

P-code (Precision) which is encrypted for military and other

authorised users.

L2 1227.60 MHz

L2 is modulated by the P-code and, beginning with Block IIR-M

satellites, the L2C (civilian) code. L2C, is considered ―under

development‖ and forms part of the GPS modernisation

process (discussed at a later stage).

L5 1176.45 MHz

At the moment, L5 is available for demonstration on one GPS

satellite, which is also considered part of the GPS

modernisation process (discussed at a later stage).

The GPS control segment consists of a master control station (and a back-up master control station)

and monitor stations throughout the world, as shown in the graphic below. Four monitor stations were

implemented early in the NAVSTAR programme, and then six more NGA (National Geospatial

Intelligence Agency, also part of the US Department of Defence) stations were added in 2005.

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The monitor stations track the satellites via their broadcast signals, which contain satellite ephemeris

data, ranging signals, clock data and almanac data. These signals are passed to the master control

station where the ephemerides are re-calculated. The resulting ephemeride and timing corrections are

transmitted back up to the satellites through data up-loading stations.

GPS Control Segment

GPS reached Fully Operational Capability in 1995. In 2000, a project was initiated to modernise the

GPS space and ground segments, to take advantage of new technologies and user requirements.

Space segment modernisation has included new signals, as well as improvements in atomic clock

accuracy, satellite signal strength and reliability. Control segment modernisation includes improved

ionospheric and tropospheric modelling and in-orbit accuracy, and additional monitoring stations. User

requirement has also evolved, to take advantage of space and control segments improvement.

The latest generation of GPS satellites has the capability to transmit a new civilian signal, designated

L2C. Once operational, L2C will ensure the accessibility of two civilian codes. L2C will be easier for

the user segment to track and it will provide improved navigation accuracy. It will also provide the

ability to directly measure and remove ionospheric delay error for a particular satellite, using the

civilian signals on both L1 and L2.

The US has started implementing a third civil GPS frequency (L5) at 1176.45 MHz. The first

NAVSTAR GPS satellite to transmit L5, on a demonstration basis, was launched in 2009. The

benefits of the L5 signal include meeting the requirements for critical safety-of-life applications such

as that needed for civil aviation, and providing improved ionospheric correction, signal redundancy,

improved signal accuracy and improved interference rejection.

In addition to the new L2C and L5 signals, GPS satellite modernisation includes a new military signal

and an improved L1C which will be backward compatible with L1 and which will provide greater

civilian interoperability with Galileo.

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2.6 GLONASS (Global Navigation Satellite System)

―GLObal‘naya NAvigatsionnaya Sputnikovaya Sistema‖ or translated into

English as ―GLObal NAvigation Satellite System‖ is a radio-based satellite

navigation system, developed by the former Soviet Union as an

experimental military communications system during the 1970‘s. When the

Cold War ended, the Soviet Union recognised that GLONASS had

commercial applications, through the system‘s ability to transmit weather

broadcasts, communications, navigation and reconnaissance data.

The first GLONASS satellite was launched in 1982 and the

system was declared fully operational in 1993. After a period

where GLONASS performance declined, Russia committed to

bringing the system up to the required minimum of 18 satellites.

The Russian government set 2011 as the date for full deployment

of the 24-satellite constellation and has ensured that the

necessary financial support will be there to meet this date.

GLONASS satellites have evolved since the first ones were

launched. The latest generation, GLONASS-M satellite is shown

in the graphic on the right.

GLONASS-M Satellite in Final Manufacturing

The GLONASS constellation provides visibility to a variable number of satellites, depending on your

location. A minimum of four satellites in view allows a GLONASS receiver to compute its position in

three dimensions and to synchronise with system time.

The GLONASS space segment is summarised in the table below.


Satellites 21 plus 3 spare

Orbital planes 3

Orbit inclination 64.8⁰


When complete, the GLONASS space segment will consist of 24 satellites in three orbital planes, with

eight satellites per plane. The GLONASS constellation geometry repeats about once every eight

days. The orbit period of each satellite is approximately 8/17 of a sidereal day so that, after eight

sidereal days, the GLONASS satellites have completed exactly 17 orbital revolutions.

Each orbital plane contains eight exactly spaced satellites. One of the satellites will be at the same

spot in the sky at the same sidereal time each day. The satellites are placed into nominally circular

orbits with target inclinations of 64.8° and an orbital radius of 25 510 km, about 1 050 km lower than

GPS satellites.

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The GLONASS satellite signal identifies the satellite and includes:

Positioning, velocity and acceleration information for computing satellite locations.

Satellite health information.

Offset of GLONASS time from UTC (SU) – formerly Soviet Union and now Russia.

Almanac of all other GLONASS satellites.

The GLONASS control segment consists of the system control centre and a network of command

tracking stations across Russia. The GLONASS control segment, similar to that of GPS, monitors the

status of satellites, determines the ephemeride corrections, and satellite clock offsets with respect to

GLONASS time and UTC (Coordinated Universal Time). Twice a day, it uploads corrections to the

satellites.

The table below summarises the GLONASS signals.

GLONASS Signal Characteristics

Designation Frequency Description

L1 1598.0625 –

1609.3125 MHz

L1 is modulated by the HP (high precision) and the SP

(standard precision) signals.

L2 1242.9375 –

1251.6875 MHz

L2 is modulated by the HP and SP signals. The SP signal is

identical to that transmitted on L1.

GLONASS satellites each transmit on slightly different L1 and L2 frequencies, with the P-code (HP

code) on both L1 and L2, and the C/A code (SP code), on L1 (all satellites) and L2 (most satellites).

GLONASS satellites transmit the same code format at different frequencies, a technique known as

FDMA, for frequency division multiple access. Note that this is a different technique from that used by

GPS.

GLONASS signals have the same polarisation (orientation of the electromagnetic waves) as GPS

signals, and have comparable signal strength.

The GLONASS system is based on 24

satellites using 12 frequencies. It

achieves this by having antipodal

satellites transmitting on the same

frequency. Antipodal satellites are in

the same orbital plane but are

separated by 180⁰. The paired

satellites can transmit on the same

frequency because they will never

appear at the same time in view of a

receiver on the Earth‘s surface as

shown in the graphic on the right.

GLONASS Antipodal Satellites

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The use of GLONASS in addition to GPS, results in there being a larger number of satellites in the

field of view, which has the following benefits:

Reduced signal acquisition time;

Improved position and time accuracy;

Reduction of problems caused by obstructions such

as buildings and foliage;

Improved spatial distribution of visible satellites,

resulting in improved dilution of precision (discussed

at a later stage).

To determine a position in GPS-only mode, a receiver

must track a minimum of four satellites. In combined

GPS/GLONASS mode, the receiver must track five

satellites, at least one of which must be a GLONASS

satellite so that the receiver can determine the

GPS/GLONASS time offset. With the availability of

combined GPS/GLONASS receivers, users have access

to a satellite combined system with over 40 satellites.

Performance in urban canyons and other locations with

restricted visibility improves as more satellites are

accessible by the receiver.

Combined GPS/GLONASS receiver

2.7 GALILEO (The name given to the European Global Navigation Satellite System)

Galileo, Europe‘s planned global navigation satellite system, will provide a

highly accurate and guaranteed global positioning system under civilian

control. The United States and European Union have been co-operating

since 2004 to ensure that GPS and Galileo are compatible and

interoperable at the user level.

By offering dual frequencies as standard, Galileo will deliver real-

time positioning accuracy down to the metre range, previously

not achievable by a publicly available system. Galileo will

guarantee availability of service under all but the most extreme

circumstances and it will inform users within seconds of a failure

of any satellite. This will make it suitable for applications where

safety is crucial, such as in air and ground transport.

The first experimental Galileo satellite (GIOVE-A), part of the

Galileo System Test Bed (GSTB) was launched in December

2005. The purpose of this experimental satellite is to characterise

critical Galileo technologies, which are already in development

under European Space Agency (ESA) contracts.

Preparing to launch the Soyuz-FG rocket with the Galileo satellite

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Four operational satellites are planned to be launched in the 2010-2012 time frame to validate the

basic Galileo space and ground segment. Once this In-Orbit Validation (IOV) phase has been

completed, the remaining satellites will be launched, with plans to reach Full Operational Capability

(FOC) likely sometime after 2013.

The Galileo space segment is summarised in the table below.


Satellites 27 operational and 3 active spares

Orbital planes 3



Once the constellation is operational, Galileo navigational signals will provide coverage at all latitudes.

The large number of satellites, together with the optimisation of the constellation and the availability of

the three active spare satellites, will ensure that the loss of one satellite has no discernable effect on

the user segment.

Two Galileo Control Centres (GCC), which are to be located in Europe, will control the satellites. Data

recovered by a global network of twenty Galileo Sensor Stations (GSS) will be sent to the GCC

through a redundant communications network. The GCC will use data from the sensor stations to

compute integrity information and to synchronise satellite time with ground station clocks. Control

centres will communicate with the satellites through up-link stations, which will be installed around the

world.

Galileo will provide a global Search and Rescue (SAR) function, based on the operational search and

rescue satellite-aided Cospas-Sarsat system. To do this, each Galileo satellite will be equipped with a

transponder that will transfer distress signals to the Rescue Co-ordination Centre (RCC), which will

then initiate the rescue operation. At the same time, the system will provide a signal to the user,

informing them that their situation has been detected and that help is underway. This latter feature is

new and is considered a major upgrade over existing systems, which do not provide user feedback.

Five Galileo services are proposed, as summarised in the table below.

Table: Galileo Services

Service Description

Free Open Service (OS)

Provides positioning, navigation and precise timing service. It will be

available for use by any person with a Galileo receiver. No

authorisation will be required to access this service. Galileo is

expected to be similar to GPS in this respect.

High reliable Commercial

Service (CS)

Service providers can provide added-value services, for which they

can charge the end customer. The CS signal will contain data relating

to these additional commercial services.

Safety-of-Life Service

(SOL)

Improves on OS by providing timely warnings to users when it fails to

meet certain margins of accuracy. A service guarantee will likely be

provided for this service.

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Service Description

Government encrypted

Public Regulated Service

(PRS)

Highly encrypted restricted-access service offered to government

agencies that require a high availability navigation signal.

Search and Rescue Service

(SAR)

Public service designed to support search and rescue operations,

which will make it possible to locate people and vehicles in distress.

2.8 Other Navigation Satellite Systems

2.8.1 China

The Beidou Navigation System (or Beidou Satellite

Navigation and Positioning System) is a project by China to

establish an independent satellite navigation system. The

current Beidou-1 system (made up of four satellites) is

experimental and has limited coverage and application.

However, China has started the implementation of a GNSS known as Compass or Beidou-2.

The initial system will provide regional coverage. The target is that this be followed after 2015

with the implementation of a constellation of GEO (geostationary orbit) and MEO (Medium

Earth Orbit) satellites that will provide global coverage, as shown in the table below:

Table: Planned Compass Satellite Constellation

Satellites 35, a combination of 5 GEO and 30 MEO

Orbital planes 6



The Beidou Navigation System is named after the Big Dipper constellation, which is known in

Chinese as Běidǒu. The name literally means "Northern Dipper", the name given by Chinese

astronomers to the seven brightest stars of Ursa Major or ―the Great Bear‖ constellation.

Historically, this set of stars was used in navigation to locate the North Star Polaris. As such,

Beidou also serves as a metaphor for the purpose of the satellite navigation system.

Unlike the GPS, GLONASS and Galileo systems, which use medium Earth orbit (MEO)

satellites, Beidou-1 uses satellites in geostationary orbit (GEO). This means that the system

does not require a large constellation of satellites, but it also limits the coverage areas on

Earth where the satellites are visible. The area that can be serviced is from 70°E to 140°E

and from 5°N to 55°N.

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Coverage Polygon of Beidou-1

As mentioned above, the Beidou-1 satellites (1A, 1B, 1C and 1D), were designed as

experimental satellites. The new system (Compass or Beidou-2) will be a constellation of 35

satellites, which include five geostationary orbit satellites, for backward compatibility with

Beidou-1, and 30 medium Earth orbit satellites, that will offer complete coverage of the globe.

There will be two levels of service provided; free service for those in China, and licensed

service for the military:

The free service will have a 10-metre location-tracking accuracy, will synchronise clocks

with an accuracy of 50 ns, and measure speeds within 0.2 m/s.

The licensed service will be more accurate than the free service, can be used for

communication, and will supply information about the status to the users.

Three satellites for Compass have been launched in 2007, 2009 and also early in 2010. In the

next few years, China plans to continue setting up the system for global operation from 2017

with 30 satellites. Regional operation within Asia Pacific would be completed with more than

10 satellites in late 2012.

Table: Beidou-1 and Compass Satellites

Date Launcher Satellite Orbit Usable

31/10/2000 LM-3A Beidou-1A GEO 140°E Unclear

21/12/2000 LM-3A Beidou-1B GEO 80°E Unclear

25/05/2003 LM-3A Beidou-1C GEO 110.5°E Unclear

03/02/2007 LM-3A Beidou-1D De-orbited No

14/04/2007 LM-3A Compass-M1 MEO 21 500 km Yes

15/04/2009 LM-3C Compass-G2 GEO drifting No

17/01/2010 LM-3C Compass-G1 GEO 144.5°E Yes

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The frequencies for Compass are allocated in four bands: E1, E2, E5B and E6; and overlap

with Galileo. The overlapping is convenient from a receiver design point of view, but it does

raise the issues of inter-system interference, especially within E1 and E2 bands, which are

allocated for Galileo‘s publicly-regulated service. However, under International

Telecommunications Union (ITU) policies, the first nation to start broadcasting in a specific

frequency will have priority to that frequency, and any subsequent users will be required to

obtain permission prior to using that frequency, and otherwise ensure that their broadcasts do

not interfere with the original nation's broadcasts. It now appears that Chinese Compass

satellites will start transmitting in the E1, E2, E5B, and E6 bands before Europe's Galileo

satellites and thus have primary rights to these frequency ranges.

Galileo, GPS and Compass Frequency Allocation

2.8.2 India

The Indian Regional Navigation Satellite System (IRNSS) is an autonomous regional satellite

system being developed by Indian Space Research Organisation, which would be under total

control of the Indian government. The government approved the project in May 2006, with the

intention of the system to be completed and implemented by 2014. It will consist of a

constellation of seven navigation satellites. The first satellite, of the proposed constellation, is

expected to be launched in the last quarter of 2011 with subsequent six months periodic

launches taking place. It means the IRNSS will be optimally functional by 2014.

The proposed system would consist of a constellation of seven satellites and a support

ground segment. Three of the satellites in the constellation will be placed in geostationary

orbit. These GEOs will be located at 34°E, 83°E and 132°E. These satellites will orbit with a

24 000 km apogee and a 250 km perigee inclined at 29°. Two of the satellites will cross the

equator at 55°E and two at 111°E. Such an arrangement would mean all seven satellites

would have continuous radio visibility with Indian control stations. The satellite payloads

would consist of atomic clocks and electronic equipment to generate the navigation signals.

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Schematic of Proposed IRNSS Deployment

The navigation signals would be transmitted in the S-band frequency (2 – 4 GHz) and

broadcast through a phased array antennae to maintain required coverage and signal

strength.

The system is intended to provide an all-weather absolute position accuracy of better than 7.6

metres throughout India and within a region extending approximately 1 500 km around it. A

goal of complete Indian control has been stated, with the space segment, ground segment

and user receivers all being built in India. The ground segment of IRNSS constellation would

consist of a Master Control Centre (MCC), ground stations to track and estimate the satellites‘

orbits and ensure the integrity of the network, and additional ground stations to monitor the

health of the satellites with the capability of issuing radio commands to the satellites. The

MCC would estimate and predict the position of all IRNSS satellites, calculate integrity, make

necessary ionospheric and clock corrections and run the navigation software. In pursuit of a

highly independent system, an Indian standard time infrastructure would also be established.

2.8.3 Japan

The Quasi-Zenith Satellite System (QSSS), or ―Juntencho‖ in Japanese, is a proposed three-

satellite regional time transfer system and enhancement for the GPS that will be receivable

within Japan. Full operational status is expected by 2013, with the first satellite scheduled for

launch in 2010.

QSSS is targeted at mobile applications, to provide communications-based services (video,

audio and data) and positioning information. With regards to its positioning service, QSSS

would only provide limited accuracy on its own and is not currently required in its

specifications to work in a stand-alone mode. As such, it is viewed as a GNSS augmentation

service.

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The satellites would be placed in a

periodic Highly Elliptical orbit (HEO).

These orbits allow the satellites to

dwell for more than 12 hours a day

with an elevation above 70°

(meaning they appear almost

overhead most of the time) and give

rise to the term ―quasi-zenith‖ for

which the system is named. As of

June 2003, the proposed orbits

ranged from 45° inclination with little

eccentricity, to 53° with significant

eccentricity.

QSSS Orbit

QSSS can enhance GPS services in two ways: first, availability enhancement, whereby the

availability of GPS signals is improved; second, performance enhancement whereby the

accuracy and reliability of GPS derived navigation solutions is increased.

Because the GPS availability enhancement signals transmitted from the Quasi-Zenith

satellites (QSSs) are compatible with modernised GPS signals, and hence interoperability is

ensured, the QSSs will transmit the L1C signal, L2C signal and L5 signal. This minimises

changes to specifications and receiver designs.

2.8.4 France

Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a French

satellite system used for the determination of satellite orbits (e.g. TOPEX/Poseidon) and for

positioning.

It uses the ―Doppler Effect‖ as principle of operation: a so-called beacon is installed on the

ground and it emits a radio signal, which is received by the satellite. A frequency shift of the

signal occurs that is caused by the movement of the satellite (Doppler Effect). From this

observation, satellite orbits, ground positions, as well as other parameters can be derived.

There are about 50 – 60 stations equally distributed over the Earth which ensures a good

coverage for orbit determination. For the installation of a beacon only electricity is required

because the station only emits a signal, but does not receive any information. Therefore it is

possible to install beacons in remote areas such as the Mount Everest base camp.

The best known satellites equipped with DORIS are the two altimetry satellites

TOPEX/Poseidon and Jason. They are used to observe the ocean surface as well as currents

or wave heights. DORIS contributes to their orbit accuracy of about 2 cm.

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TOPEX/Poseidon and Jason Satellite Series

Other DORIS satellites are the European Remote-Sensing Satellite (ERS) and SPOT

(Satellite Pour l‘Observation de la Terre) satellites.

Life-size Model of the ERS-2 Satellite (left) and SPOT-5 Satellite (right)

Apart from orbit determination the DORIS observations are used for positioning of ground

stations. The accuracy is a bit lower than with GPS, but it still contributes to the International

Terrestrial Reference Frame (ITRF).

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3 ALL WEATHER OPERATION

All weather operations refers to the practice of instrument flying (IF) and the associated procedures as

applied during flight under instrument flight rules (IFR). An instrument approach or instrument

approach procedure (IAP) is a type of air navigation that allows a pilot to fly an aircraft to a position

from which a landing may be effected under reduced visibility conditions (known as instrument

meteorological conditions or IMC), or to reach visual conditions permitting a visual approach and

subsequent landing. IAPs fall into one of two categories. Firstly and also the more commonly used is

the pilot interpreted approach procedure (ILS, VOR and NDB approaches). Secondly and used

infrequently by civilian commercial operators is the ATC interpreted approach procedure (surveillance

radar approach – SRA, ground controlled approach – GCA and the oldest of them all the VDF cloud

brake procedures). Pilot interpreted approaches are classified as either precision or non-precision,

depending on the accuracy and capabilities of the navigational aids (NAVAIDs) used. Precision

approaches utilise both lateral (localiser) and vertical (glide slope) information. Non-precision

approaches provide lateral course information only.

The publications depicting instrument approach procedures are called Terminal Procedures, but are

commonly referred to by pilots as "approach plates". These documents graphically depict the specific

procedure to be followed by a pilot for a particular type of approach to a given runway. They depict

prescribed altitudes and headings to be flown, as well as obstacles, terrain, and potentially conflicting

airspace. In addition, they also list missed approach procedures and commonly-used radio

frequencies.

Instrument approaches are generally designed such that a pilot of an aircraft in instrument

meteorological conditions (IMC), by the means of radio, GNSS or INS navigation with no assistance

from air traffic control, can navigate to the airport, hold in the vicinity of the airport if required, then fly

to a position from where sufficient visual reference of the runway may be established to allow landing

to be made, or execute a missed approach if the required visual contact with the aerodrome and/or

runway periphery is not established. The whole of the approach is defined and published in this way

so that instrument approaches may be completed procedurally at airports where air traffic control

does not use radar or in the case of radar failure.

Instrument approaches generally involve five phases of flight:

Arrival: where the pilot navigates to the

Initial Approach Fix (IAF: a NAVAID or

reporting point), and where holding can

take place.

Initial Approach: the phase of flight after

the IAF, where the pilot commences the

navigation of the aircraft to the Final

Approach Fix (FAF), a position aligned

with the runway, from where a safe

controlled descent back towards the

airport can be initiated.

Intermediate Approach: an additional

phase in more complex approaches that

may be required to navigate to the FAF.

Final approach: between 4 and 12 NMs of straight flight descending at a set rate (usually an angle

of between 2.5 and 6⁰).

Missed Approach: an optional phase; should the required visual reference for landing not have

been obtained at the end of the final approach, this allows the pilot to climb the aircraft to a safe

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altitude and navigate to a position to hold for weather improvement, from where another approach

can be commenced or the decision to divert may be taken.

When aircraft are under radar control, air traffic controllers may replace some or all of these phases of

the approach with radar vectors to the final approach. This is done to allow traffic levels to be

increased from what is possible when a fully procedural service is being provided. It is very common

for air traffic controllers to vector aircraft to the final approach aid, e.g. the ILS, which is then used for

the final approach. In the case of the rarely-used Ground Controlled Approach, the instrumentation

(normally Precision Approach Radar) is on the ground and monitored by a controller, who then issues

precise instructions for the adjustment of heading and altitude of the aircraft to the pilot flying the

approach.

3.1 Conventional NAVAID Based Procedures

There are a number of different procedures available at the moment, all based on conventional

NAVAIDs including VDF, NDB, VOR, SRA, ILS, GCA.

3.1.1 Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs)

Standard Instrument arrival and departure procedures are designed in such a way that they

require aircraft to fly (track) either directly away from or directly to a beacon. Some

procedures may even require the pilot to

intercept and then follow a DME arc, or

whilst tracking towards one beacon,

execute a turn at a published DME range

and then intercept a track to another

beacon. One of the reasons for designing

these standard instrument routings is to

reduce the need for ATCs to vector

aircraft, another reason is to reduce the

amount of radio transmissions between

ATC and pilot.

A STAR usually covers the phase of a

flight that lies between the top of descent

from cruise or en-route flight and the final

approach to a runway for landing. A

typical STAR consists of a set of starting

points, called transitions, and a

description of routes (typically via

waypoints) from each of these transitions

to a point near a destination airport, upon

reaching which the aircraft can join an

instrument approach (IAP) or be vectored

for a final approach by the approach

controller. Sometimes several airports in

the same area may share a single STAR,

in such cases aircraft destined for any of

the airports served by the particular STAR will follow the same arrival route up until reaching

the final waypoint, after which they join approaches for their respective destination airports.

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STARs can be very detailed (as is often the case in Europe), allowing pilots to go from the

start of the descent to the final approach entirely on their own once ATC has cleared them for

the arrival, or they can be more general (as is often the case in the United States), providing

guidance to the pilot which is then supplemented by instructions from ATC.

Just like the STAR, a SID is normally developed to reduce both pilot and ATC workload and

aims to regulate and streamline the traffic flow out of an airport or area. SIDs are designed to

be easy to understand and if possible limited to one page. Although a SID will keep aircraft

away from terrain, it is optimised for ATC route of flight and will not always provide the most

efficient climb, but aims to strike a balance between obstacle avoidance and airspace

considerations.

3.1.2 The Non-Precision Approach

(NPA)

The NPA is the oldest type of

instrument approach used.

Today there are two categories

of NPAs, firstly and most

commonly used are the pilot

interpreted NPAs and secondly,

the less frequently used ATC

interpreted surveillance radar

approach (SRA).The NPA was

developed to allow an aircraft to

transition from the cruise phase

of flight, most often via a

descent leg, holding pattern

and a final descent leg to a

position on final approach from

where the aircraft may ―break

cloud‖, the pilot establish visual

contact with the runway and/or

the aerodrome environment

and affect a landing with visual

reference to the ground.

The first and most often used,

the pilot interpreted NPA, may

be based on one of two

NAVAIDs, either a NDB or a

VOR. These approaches offer

only lateral guidance with no

form of vertical guidance being

offered from the NAVAID itself.

For this type of approach the pilot will manage the vertical navigation of the aircraft-based on

reference to the barometric altitude (aircraft altimeter) of the aircraft and published crossing

altitudes/heights along the NPA. This type of operation results in what is known as a ―dive and

drive‖ approach. This ―dive and drive‖ procedure has been found to be the single biggest

cause of controlled flight into terrain (CFIT) accidents.

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The SRA dictates that a radar

service must be available for

this service to be offered to an

arriving aircraft. There is also a

requirement for specific

controller training that must

have been completed as well

as an approved SRA procedure

published in the AIP, before an

ATC at a suitably equipped air

traffic service unit (ATSU)

would be allowed to offer this

type of service. Give guidance

only in azimuth (lateral) no

vertical guidance.

By their design, all NPAs suffer

from two major drawbacks. The

first is that the missed approach

point and minimum descent

altitude will always leave the

aircraft very high with regard to

the ideal 3⁰ glide slope and thus

very close to the runway

threshold. This close and high

position requires very

aggressive handling to affect a

landing but results in an

unstable, high rate of descent

approach and all this in the last

500‘ above the runway. This is

why this type of approach has

resulted in such a disproportionally high number of CFIT accidents as compared to precision

approaches.

3.1.3 The Precision Approach (PA)

The NPA, though useful as an early development to enable all weather operation, proved to

be limited in its ability to facilitate continued operation in really poor weather conditions. Early

on the demand for an approach aid that offered better usability than the NDB or VOR

approach lead to the development of what we now know as a precision approach (PA). The

PA, like the NPA, was and still is available as either a pilot interpreted (ILS) or ATC

interpreted (GCA) approach. In the middle to late forties the ICAO accepted the then new

instrument landing system (ILS) as the most effective and reliable method allowing approach

and landing operation in condition of low cloud (as low as 200‘ agl) and poor visibility (as low

as 800m) for commercial operation. The ILS is the dominant approach aid at civilian

aerodromes while most military installation worldwide has developed and retained GCA

capability in tandem with ILS deployment.

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a. Instrument Landing System (ILS).

ILS forms an integral part of AST service delivery,

is widely used and will remain widely in use well

beyond 2020. The reason for this is because the

ground and airborne equipment is readily

available, relatively cheap to install and maintain

and very familiar to all operators.

An ILS approach (from the basic CAT I to the

most enabling CAT III) although very useful and

able to support continued flight operations in

extremely poor weather conditions, still have a

few fundamental restrictions. One of these

restrictions is that an ILS requires the final

approach track to be aligned with runway centre

line from at least 10 NM out. This means that the

use of an ILS in confined areas is problematic

(e.g. at aerodromes situated in very mountainous

terrain like to Alps).

Although the ILS offers an effecting solution

during most IMC days, the capability to offer and operate under Cat II and lower minima is

very costly and offset against operator profitability often does not make business sense.

Operators often choose to make passengers wait, rather than pay for Cat II capability to be

maintained for 365 days and used for a few approaches on a few days per year.

b. Micro-Wave Landing System (MLS).

A microwave landing system (MLS) is an all-

weather, precision landing system originally

intended to replace or supplement instrument

landing systems (ILS). MLS has a number of

operational advantages, including a wide

selection of channels to avoid interference with

other nearby airports, excellent performance in all

weather, and a small "footprint" at the airports.

Although some MLS systems became operational

in the 1990s, the widespread deployment initially

envisioned by its designers never became a

reality. Since its introduction most existing MLS

systems in North America have been turned off.

The integrity and continuity of service of the MLS

signal-in-space does possess the necessary

characteristics to support Cat II and Cat III, as

does the ILS.

MLS continues to be of some interest in Europe,

where concerns over the availability of GPS

http://en.wikipedia.org/wiki/Instrument_landing_system

http://en.wikipedia.org/wiki/Instrument_landing_system

http://en.wikipedia.org/wiki/Instrument_Landing_System

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continue to be an issue. A widespread installation in the United Kingdom is currently

underway, which included installing MLS receivers on most British Airways aircraft, but the

continued deployment of the system is in doubt. NASA operates a similar system called the

Microwave Scanning Beam Landing System to land the Space Shuttle.

Australia, in 1979 manufactured MLS systems that were subsequently deployed in the US,

EU, Taiwan, China and Australia. The CAA in UK developed a version of the MLS which is

installed at Heathrow and other airports due to the greater incidence of instrument

approaches and Cat II/III weather there.

Compared to the existing ILS system, MLS had significant advantages. The antennas were

much smaller, due to using a higher frequency signal. They also did not have to be placed at

a specific point at the airport, and could "offset" their signals electronically. This made

placement at the airports much simpler compared to the large ILS systems, which needs to

be placed at the ends of the runways and along the approach path.

Another advantage was that the MLS signals covered a very wide fan-shaped area off the

end of the runway, allowing controllers to vector aircraft in from a variety of directions or guide

aircraft along a segmented approach. In comparison, ILS required the aircraft to fly down a

single straight line, requiring controllers to distribute planes along that line. MLS allowed

aircraft to approach from whatever direction they were already flying in, as opposed to having

to ―hold‖ before being vectored to "capturing" the ILS signal. This was particularly interesting

to larger airports, as it potentially allowed the aircraft to be separated horizontally until much

closer to the airport. Similarly in elevation, the fan shape coverage allows for variation in

approach angle making MLS particularly suited to aircraft with steep approach angles such as

helicopters, fighters and the space shuttle.

Unlike ILS, which required a variety of frequencies to broadcast the various signals, MLS

used a single frequency, broadcasting the azimuth and altitude information one after the

other. This reduced frequency contention, as did the fact that the frequencies used were well

away from FM broadcasts, another problem with ILS. Additionally, MLS offered two hundred

channels, making the possibility of contention between airports in the same area extremely

remote.

Finally, the accuracy was greatly improved over ILS. For instance, standard DME equipment

used with ILS offered range accuracy of only +/- 1200 feet. MLS improved this to +/- 100 ft in

what they referred to as DME/P (P for precision), and offered similar improvements in azimuth

and altitude. This allowed MLS to guide the extremely accurate CAT III approaches, whereas

this normally required expensive ground-based high precision radar.

Similar to other precision landing systems, lateral and vertical guidance may be displayed on

conventional course deviation indicators or incorporated into multipurpose cockpit displays.

Range information can also be displayed by conventional DME indicators and also

incorporated into multipurpose displays.

3.2 Continuous Descent Approach (CDA)

CDA finds application in two areas, first between TOD and FAF and second between the FAF

and Missed approach point or landing.

http://en.wikipedia.org/wiki/British_Airways

http://en.wikipedia.org/wiki/NASA

http://en.wikipedia.org/wiki/Microwave_Scanning_Beam_Landing_System

http://en.wikipedia.org/wiki/Space_Shuttle_program






http://en.wikipedia.org/wiki/FM



http://en.wikipedia.org/wiki/Distance_Measuring_Equipment


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The CDA concept is used during a NPA to replace the ―dive and drive method‖ of vertical

profile management with a continuous descent from the FAF to the missed approach point.

This done to reduce the risk of controlled flight into terrain (CFIT) accidents.

During the descent from cruise to the FAF the CDA concept is used to save fuel and reduce

the noise impact of the flight. To gain the maximum benefit from the application of a CDA, the

pilot needs to know the track miles to touch down and that the track to final approach will

remain set. In an ideal world this requires that arriving traffic be sequenced and that the

arrival rate and sequence be known to ATC and the Flight deck before the descent is

commenced. For the CDA concept to work ATC must allow aircraft continuous descend from

TOD to touch down. Aircraft RNAV systems are and have been able to calculate TOD based

on CDA profile taking aircraft performance into account.

3.3 Non-Conventional NAVAID Based Procedures (RNAV Approaches)

The intention with RNAV approaches

was to negate the requirement to have

aircraft fly directly to or from a ground-

based NAVAID or along a DME arc

during the descent, approach and

landing phases of flight. Aircraft have

had the ability to perform RNAV

operations from the time the flight

navigators were removed from the

flight deck, this means from the time

the British Comment and American

Boeing 707 first flew. At that time the

navigation performance accuracy was,

undefined, unregulated and wholly

misunderstood by ATC. This was the

case until the 1980s when operators

started demanding to be allowed to

develop the RNAV capabilities of the

aircraft and ATC was required to

improve airspace utilisation. RNAV

concepts were first incorporated into

oceanic airspace and then later in

continental en-route airspace. This

brought some benefit to operators and

airspace utilisation but also served to

highlight the gross inefficiencies of

terminal operation. There are a

number of problem areas in terms of

―traditional‖ terminal operations, these

include but are not limited to;

inconsistent arrival and departure routes which makes fuel planning difficult,

increased work load for both ATC and flight crew due to extensive holding followed by

incessant vectoring that,

most often results in inefficient flight profiles requiring extended downwind legs to be

flown in very inefficient configurations resulting in,

ATNS/HO/C09/30/02/01 of 184 14 July 2010

high fuel burns,

extensive noise and environmental pollution and

adding to airspace congestion.

3.3.1 Overlay Procedures Concept

Early attempts to improve terminal operations resulted in ―overlay‖ RNAV procedures being

developed that would initially ―shadow‖ conventional terminal procedures. These overlay

RNAV procedures brought no benefit or improvement to the situation and appeared to be a

waste of time and effort. The reason why no benefit was gained from this was because these

new procedures differed from the conventional procedures only in as much as the definition of

the waypoints was changed from using conventional ground-based beacons to using ―RNAV

waypoints‖. The drive to develop and implement these overlay RNAV procedures had a few

fundamental flaws that meant these overlay procedures would never be able to realise the

anticipated benefits. To ultimately realise the expected benefits from terminal RNAV

procedures the terminal operational concept needed to change completely. The RNAV

operation itself needed to be clearly regulated to ensure accuracy, integrity and continuity, the

airspace concept needed to clearly define the navigation specification and the ATM system

needed to be redefined to allow for and effectively incorporate automated flow management

capabilities. One of the fundamental RNAV capabilities that was never employed effectively

was the required time of arrival (RTA) capability. The RTA capability combined with the ability

of the RNAV system to calculate TOD based on the CDA concept means that the flight deck

system is now and has been able for a long time to calculate the most efficient descend

profile while being able to fly any published RNAV STAR.

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3.3.2 Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs)

RNAV SIDs and STARs, if developed correctly will increase airspace capacity, reduce, if not

totally eliminate conflict between arrival and departure routes, reduce both ATC and pilot

workload and reduce, if not totally eliminate the need to vector aircraft in terminal airspace.

ATNS/HO/C09/30/02/01 of 184 14 July 2010

a. Open & Closed Standard Terminal Arrival Routes (STARs).

RNAV STARs allow one of two types of terminations. The one is an open termination and the

other is a closed termination.

An open STAR is simply put a STAR that terminates in ATC vectors being provided onto the

final approach segment. This final approach segment is typically a pilot interpreted PA (an

ILS).

Merging of arrival flows with open loop radar vectors at PARIS CDG, 2002

A closed STAR is one where no ATC vectoring is required, the STAR will place the aircraft

onto the ILS through the published procedure.

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Both the open and closed STAR has a built-in track lengthening or shortening ability, but the

actual route that the aircraft will fly while on the STAR will be known to both the ATC and the

pilot before the aircraft commences the descent. This route is determined by an automated

ATM flow management function.

ATNS/HO/C09/30/02/01 of 184 14 July 2010

The “point merge” method;

Maintains flexibility to be able to expedite or delay

aircraft,

Keeps aircraft on Flight Management System

trajectory,

Maximises runway throughput

ATNS/HO/C09/30/02/01 of 184 14 July 2010

3.3.3 Sensor Specific Area Navigation (RNAV) Procedures

a. RNAV 5 (in Europe referred to and applied as Basic-RNAV aka B-RNAV).

B-RNAV requires aircraft conformance to a track keeping accuracy of ± 5 NM for at least 95%

of flight time to ensure that the capacity gains are achieved whilst meeting the required safety

targets. B-RNAV can be achieved using inputs from VOR/DME, DME/DME or GPS. (INS may

be used for up to 2 hours after the last radio beacon or on-ground update. B-RNAV

requirements became mandatory in ECAC airspace on 23 April 1998 on the entire ATS route

network above FL 95. B-RNAV is already being used on selected routes into and out of

terminal airspace in some States.

i. What is B-RNAV?

RNAV is a method of navigation which permits aircraft operations on any desired flight path

within the coverage of station referenced navigation aids or within the limits of the capability of

self-contained aids, or a combination of these. Airborne RNAV equipment automatically

determines aircraft position by processing data from one or more sensors and guides the

aircraft in accordance with appropriate routing instructions. Position can be displayed to the

pilot in various ways, most practically in terms of the aircraft position relative to the pre-

computed desired track. Most RNAV equipment can employ any lateral displacement of the

aircraft from the desired track to generate track guidance signals to the auto-pilot. With other

less sophisticated RNAV equipment manual corrective action is taken by the pilot.

B(asic)-RNAV defines European RNAV operations which satisfy a required track keeping

accuracy of ± 5 NM for at least 95% of the flight time. This level of navigation accuracy is

comparable with that which can be achieved by conventional navigation techniques on ATC

routes defined by VOR/DME, when VORs are less than 100 NM apart. For the determination

of aircraft position suitable input data can be derived from the following navigation sources:

DME/DME

VOR/DME (within 62 NM VOR range)

INS (with radio beacon updating or limited to 2 hours use after last on-ground position

update)

LORAN C (with use limitations)

GPS (with use limitations)

For ECAC airspace the primary sources of navigation information are VOR/DME, DME/DME

and GPS. The availability and continuity of VOR and DME coverage have been calculated for

most of Europe and they are considered to be capable of meeting the requirements of the en-

route phase of operations.

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ii. What does B-RNAV offer?

B-RNAV operations in ECAC airspace provides a number of advantages over the

conventional ground-based navigation, whilst maintaining existing safety standards. These

advantages and their related benefits include:

(1) improved management in the flow of traffic by repositioning of intersections;

(2) more efficient use of available airspace, by means of a more flexible ATS route

structure and the application of the Flexible Use of Airspace (FUA) Concept,

permitting the establishment of:

more direct routes (dual or parallel) to accommodate a greater flow of en-route

traffic;

bypass routes for aircraft overflying high-density terminal areas;

alternative or contingency routes on either a planned or an ad hoc basis;

establishment of optimum locations for holding patterns;

optimised feeder routes;

(3) reduction in flight distances resulting in fuel savings;

(4) reduction in the number of ground navigation facilities.

All these are easily achievable. One of the main objectives of the initial application of RNAV

should be to ensure that full use is made of the existing on board RNAV systems. Many

RNAV systems have been fitted for some time and are capable of performance better than

RNP 5 accuracy. Simulations demonstrated that capacity gains up to 30% could be achieved

only by a uniform application of B-RNAV, in parallel with the revised ATS route network and

the implementation of FUA concept.

iii. Where and how could B-RNAV be implemented?

If implemented in terminal airspace the requirement will be that VOR/DME remains available

for reversionary navigation. VOR/DME must also remain available for reversionary navigation

on ATS routes in the lower airspace.

iv. Where has B-RNAV been implemented?

B-RNAV has been implemented throughout the entire ATS Route Network in the ECAC area

since 23 April 1998. B-RNAV applies to all IFR flights operating in the public transport

category, in conformity with the ICAO procedures. In some cases B-RNAV has also been

implemented on certain SIDs and STARs provided that:

(1) The B-RNAV portion of the route is above Minimum Sector Altitude/Minimum Flight

Altitude/Minimum Radar Vectoring Altitude (as appropriate), has been developed in

accordance with established PANS-OPS criteria for en-route operations and

conforms to B-RNAV en-route design principles.

(2) The initial portion of departure procedures is non-RNAV up to a conventional fix

beyond which the B-RNAV procedure is provided in accordance with the criteria

given above.

(3) The B-RNAV portion of an arrival route terminates at a conventional fix in

accordance with the criteria given above and the arrival is completed by an

alternative final approach procedure (most often the conventional ILS), also

appropriately approved.

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(4) Due regard has been taken, during the design process, of the users operating

procedures. The National Authorities may designate domestic routes in the lower

airspace, which can be used by aircraft which are not B-RNAV capable. Each State

should publish appropriate mandatory carriage requirements identifying the airspace

within which the mandate prevails. National Administrations are required to publish

the coverage of their navigation aids, to notify the status of these aids and to ensure

that the co-ordinates of all aids and waypoints are referenced to the WGS-84

geodetic reference system. Manufacturers, operators and database providers are

responsible for ensuring that RNAV systems operate in accordance with the WGS-84

system. The specific procedures for B-RNAV operations are incorporated in the

ICAO Doc 7030/4 Ed. 1997.

b. Lateral Navigation (LNAV).

LNAV refers to navigating over a ground

track with guidance from an electronic

device which gives the pilot (or autopilot)

error indications in the lateral direction

only and not in the vertical direction. In

aviation lateral navigation is of two

guidance types: linear guidance and

angular guidance. Linear means that the

left and right deviations of the aircraft are

available as a distance of the aircraft from

the desired ground track to its actual

position on either side of the desired track.

In angular guidance, the error indication is given in degrees of angle from the desired line

relative to a ground-based navigation device. To provide an illustration, as the aircraft

approaches the ground device with a constant angular error, its distance to the desired

ground line decreases. In the context of aviation instrument approaches, an LNAV approach

(one that uses lateral navigation) is implied to be a GNSS navigation signal based approach

and to have linear lateral guidance. A VOR based approach will have angular lateral

guidance.

The approach minimas for

LNAV approaches are higher

than that of ILS approaches

and higher than those for

RNAV approaches that

incorporate vertical

guidance. An aircraft

executing an LNAV

instrument approach must

descend incrementally rather

than follow a fixed glide

slope. A LNAV approach is a

type of 'non-precision'

approach. In a precision

approach there is electronic

vertical (slope) guidance down to a decision altitude (DA). In the case of the non-precision

approach, the aircraft can descend only to the minimum descent altitude or MDA. An MDA

segment is flown until the airport is in sight and the pilot can land. If the airport is not in sight

http://en.wikipedia.org/wiki/Autopilot

http://en.wikipedia.org/wiki/VHF_omnidirectional_range

http://en.wikipedia.org/wiki/RNAV

ATNS/HO/C09/30/02/01 of 184 14 July 2010

by the time the pilot reaches a missed approach point (MAP) on the MDA, a missed approach

must be initiated.

The RNAV implementation of the non-precision LNAV approach (using GNSS as navigation

signal source) may only be flown if satellite configuration at the time of the approach will

support the accuracy requirement that will allow a full scale course deviation indication of 0.3

nautical miles (about 1800 feet to the left and right or 3600 feet total) from the final approach

fix and extending uninterrupted through to the missed approach point. If this sensitivity is not

available or is lost, the pilot will be notified by the on-board receiver (via RAIM checking) and

must initiate a missed approach or continue with an alternate type of approach using an

alternate navigation reference (typically conventional NAVAIDs).

c. Barometric Vertical Navigation (Baro-VNAV) and Approach with Vertical Guidance

(APV).

VNAV in aviation is a function of autopilot which directs vertical movement of aircraft either

according to a pre-programmed FMS flight plan during cruise or according to ILS glide slope

during an approach. Vertical guidance is given with reference to barometric altitude.

VNAV in the sense that the FMS directs altitude according to a flight plan was first introduced

on B757 and B767 in 1982, while Autoland (using ILS guidance) has been available since

mid-20th century. In the USA Localiser performance with vertical guidance (LPV) are the

highest precision GPS (WAAS enabled) instrument approach procedures currently available

without specialised aircrew training requirements, such as required navigation performance

(RNP). Landing minima are similar to those in an instrument landing system (ILS), that is, a

decision altitude of 200 feet and visibility of 1/2 mile. Examples in the USA (from Garmin) are

the GNS 480, GNS 430W, 530W, and the Garmin G1000. LPV is designed to provide 16

meter horizontal accuracy and 20 meter vertical accuracy 95 percent of the time. Actual

performance has exceeded these levels. WAAS has never been observed to have a vertical

error greater than 12 meters in its operational history.

As of January 15, 2009 the Federal Aviation Administration has published 1,445 LPV

approaches at 793 airports. This is greater than the number of published Category I ILS

procedures.

3.3.4 RNP Procedures (Pre-PBN)

a. Baro-VNAV and APV.

The baro-VNAV navigation system presents the pilot with estimated vertical guidance

referenced to a specified vertical path angle (VPA), nominally of 3º. The computed vertical

guide is based on the barometric altitude and is specified as a VPA from the reference datum

height (RDH). The calculated vertical path is stored in RNAV/RNP system navigation data

base as part of the instrument flight procedure specification. For other flight phases,

barometric VNAV offers vertical guidance path information that can be defined by vertical

angles or altitudes at the procedure fixes. It should be noted that vertical navigation can be

performed without VNAV guidance in the initial and intermediate segments of an instrument

procedure. It is anticipated that aircraft authorised to conduct RNP authorisation required

http://en.wikipedia.org/wiki/Missed_approach_point

http://en.wikipedia.org/wiki/Aviation

http://en.wikipedia.org/wiki/Autopilot

http://en.wikipedia.org/wiki/Flight_plan

http://en.wikipedia.org/wiki/Cruise_(flight)

http://www.answers.com/topic/precision-approach

http://www.answers.com/topic/garmin-g1000

ATNS/HO/C09/30/02/01 of 184 14 July 2010

GN

SS

Lan

din

g S

yste

m

approach (RNP AR APCH) operations would also be considered eligible for the baro-VNAV

operations

NAVAID infrastructure. The procedure design does not have unique infrastructure

requirements. This criterion is based upon the use of barometric altimetry by an airborne

RNAV/RNP system whose performance capability supports the required operation. The

procedure design will have to take into account the functional capabilities required as

prescribed by the ICAO.

b. GNSS Landing System (GLS).

The aviation industry has been developing

a positioning and landing system based

on a GNSS. These efforts culminated in

late 2001, when the ICAO approved an

international standard for a landing system

based on RNAV using local correction of

GNSS data to a level that would support

instrument approaches. This work by the

ICAO resulted in the ICAO Standards and

Recommended Practices (SARPS) that

define the characteristics of a GBAS. The

GBAS service provides a correction signal

that can be used by suitably equipped

aircraft as the basis of a GNSS landing

system (GLS). The initial SARPS by the

ICAO supports an approach service. Future refinements should lead to full low-visibility

service (i.e., takeoff, approach, and landing) and low visibility taxi operations.

i. Elements of the GLS

The GLS consists of three major elements;

a GNSS that supports worldwide navigation position fixing,

a GBAS facility at each equipped airport that provides local navigation satellite

correction signals, and

avionics in each aircraft that process and provide guidance and control based on the

satellite and GBAS signals (fig.1).

The GLS uses a GNSS for the basic positioning service. The GPS constellation already is in

place and improvements are planned over the coming decades. The Galileo constellation was

scheduled to be available in 2008, but is not yet fully operational.

A GBAS service is used for local augmentation of the basic GNSS positioning at or near the

relevant airport via a GBAS radio transmitter facility. The GBAS corrections are transmitted

from a ground station and can be received by nearby aircraft via a VHF Data Broadcast

(VDB) data link.

As far as the development of avionics is concerned, Boeing aircraft that are currently being

produced contain Multi-Mode Receivers (MMR) that supports conventional ILS and basic

GPS operations. For the GLS application the aircraft systems only use satellite information

that is supported by correction data received from the GBAS. When the aircraft are relatively

ATNS/HO/C09/30/02/01 of 184 14 July 2010

Fig

ure

2. G

LS

Prim

ary

Nav. D

isp

lay

close to the GBAS station, the corrections are most effective, and the MMRs can compute a

very accurate position. Typical lateral accuracy is expected to be better than or equal to 1 m.

ii. GLS Operations

A single GBAS ground station typically provides approach and landing service to all runways

at the airport where it is installed. The GBAS may even provide limited approach service to

nearby airports. Each runway approach direction requires the definition of a final approach

segment (FAS) to establish the desired reference path for an approach, landing, and rollout.

The FAS data for each approach are determined by the GBAS service provider and typically

are verified after installation of the GBAS ground station.

One feature that differentiates the GLS from a traditional landing system such as the ILS is

the potential for multiple final approach paths, glide slope angles, and missed approach paths

for a given runway. Each approach is given a unique identifier for a particular FAS, glide

slope, and missed approach combination. FAS data for all approaches supported by the

particular GBAS facility are transmitted to the aircraft through the same high-integrity data link

as the satellite range correction data (i.e., through the VDB data link). The MMRs process the

pseudo range correction and FAS data to produce an ILS-like deviation indication from the

final approach path. These deviations are then displayed on the pilot‘s flight instruments (e.g.,

Primary Flight Display [PFD]) and are used by aircraft systems such as the flight guidance

system (e.g., autopilot and flight director) for landing guidance.

The ILS-like implementation of the

GLS was selected to support common

flight deck and aircraft systems

integration for both safety and

economic reasons. This

implementation helps provide an

optimal pilot and system interface

while introducing the GLS at a

reasonable cost. The use of

operational procedures similar to those

established for ILS approach and

landing systems minimises crew

training, facilitates the use of familiar

instrument and flight deck procedures,

simplifies flight crew operations

planning, and ensures consistent use

of flight deck displays and

annunciations. For example, the

source of guidance information (shown

on the PFD in fig. 2) is the GLS rather

than the ILS. The scaling of the path

deviation information on the pilot‘s displays for a GLS approach can be equivalent to that

currently provided for an ILS approach. Hence, the pilot can monitor a GLS approach by

using a display that is equivalent to that used during an ILS approach.

Figure 2 shows a typical PFD presentation for a GLS approach. The Flight Mode

Annunciation on the PFD is ―GLS‖ for a GLS approach and ―ILS‖ for an ILS approach.

http://www.boeing.com/commercial/aeromagazine/aero_21/gnss_fig2.html


ATNS/HO/C09/30/02/01 of 184 14 July 2010

Fig

ure

3. T

ypic

al G

LS

Appro

ach P

rocedure

F

igure

3. T

ypic

al G

LS

Appro

ach P

rocedure

Figure 3 shows a typical GLS approach

procedure. The procedure is similar to that used

for ILS except for the channel selection method

and the GLS-unique identifier. The approach chart

is an example of a Boeing flight-test procedure

and is similar to a chart that would be used for air

carrier operations, with appropriate specification of

the landing minima.

Figure 4 is an example of a possible future

complex approach procedure using area

navigation (RNAV), Required Navigation

Performance (RNP), and GLS procedures in

combination. Pilots could use such procedures to

conduct approaches in areas of difficult terrain, in

adverse weather, or where significant nearby

airspace restrictions are unavoidable. These

procedures would combine a RNP transition path

to a GLS FAS to the runway. These procedures

can also use GBAS position, velocity, and time

(PVT) information to improve RNP capability and

more accurately deliver the airplane to the FAS.

The GBAS is intended to support multiple levels of

service to an unlimited number of aircraft within

radio range of the VDB data link. Currently, the

ICAO has defined two levels of service:

Performance Type 1 (PT 1) service and GBAS

Positioning Service (GBAS PS). PT 1 service

supports ILS-like deviations for an instrument

approach. The accuracy, integrity, and continuity

of service for the PT 1 level have been specified to

be the same as or better than the ICAO standards

for an ILS ground station supporting Category I

approaches. The PT 1 level was developed to

initially support approach and landing operations

for Category I instrument approach procedures.

However, this level also may support other

operations such as guided takeoff and airport

surface position determination for low-visibility taxi.

The GBAS PS provides for very accurate PVT

measurements within the terminal area. This

service is intended to support FMS-based RNAV

and RNP-based procedures. The improved

accuracy will benefit other future uses of GNSS

positioning such as Automatic Dependent

Surveillance — Broadcast and Surface Movement

Guidance and Control Systems.

The accuracy of the GBAS service may support

future safety enhancements such as a high-quality



ATNS/HO/C09/30/02/01 of 184 14 July 2010

electronic taxi map display for pilot use in bad weather. This could help reduce runway

incursion incidents and facilitate airport movements in low visibility. The service also may

support automated systems for runway incursion detection or alerting.

As important as the accuracy of the GBAS service is the integrity monitoring provided by the

GBAS facility. Any specific level of RNP operation within GBAS coverage should be more

available because the user receivers no longer will require redundant satellites for satellite

failure detection (e.g., RAIM).

Because the GBAS PS is optional for ground stations under the ICAO standards, some

ground stations may only provide PT 1 service. The messages uplinked through the VDB data

link indicate whether or not the ground station supports the GBAS PS and specify the level of

service for each approach for which a channel number has been assigned. When the GBAS

PS is provided, a specific five-digit channel number is assigned to allow selection of a non-

approach-specific GBAS PS from that station. Consequently, the channel selection process

allows different users to select different approaches and levels of service.

The GBAS PS and the PT 1 service are not exclusive. If the ground station provides the

GBAS PS, selecting a channel number associated with any particular approach automatically

will enable the GBAS PS service. The receiver provides corrected PVT information to

intended aircraft systems as long as the GBAS PS is enabled. ILS-like deviations also are

available when the aircraft is close enough to the selected approach path.

The ICAO is continuing development of a specification for service levels that would support

Category II and III approaches.

iii. Benefits of the GLS

From the user perspective, the GBAS service can offer significantly better performance than

an ILS. The guidance signal has much less noise because there are no beam bends caused

by reflective interference (from buildings and vehicles). However, the real value of the GLS is

the promise of additional or improved capabilities that the ILS cannot provide. For example,

the GLS can;

provide approach and takeoff guidance service to multiple runways through a single

GBAS facility,

optimise runway use by reducing the size of critical protection areas for approach and

takeoff operations compared with those needed for ILS,

provide more flexible taxiway or hold line placement choices,

simplify runway protection constraints,

provide more efficient aircraft separation or spacing standards for air traffic service

provision, and

provide takeoff and departure guidance with a single GBAS facility.

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From the service provider perspective, the GBAS can potentially provide several significant

advantages over the ILS.

First, significant cost savings may be realised because a single system may be able to

support all runways at an airport.

Operational constraints often occur with the ILS when an Air Traffic Service provider

needs to switch a commonly used ILS frequency to serve a different runway direction.

This is not an issue with the GBAS because ample channels are available for

assignment to each approach. In addition, because the GBAS serves all runway ends

with a single VHF frequency, the limited navigation frequency spectrum is used much

more efficiently. In fact, a GBAS may even be able to support a significant level of

instrument approach and departure operations at other nearby airports.

The placement of GBAS ground stations is considerably simpler than for the ILS

because GBAS service accuracy is not degraded by any radio frequency propagation

effects in the VHF band. Unlike the ILS, which requires level ground and clear areas on

the runway, the siting of a GBAS VHF transmitter can be more flexible than ILS. GBAS

receivers do not need to be placed near a runway in a specific geometry, as is the case

with the ILS or MLS. Hence, this virtually eliminates the requirements for critical

protection areas or restricted areas to protect against signal interference on runways

and nearby taxiways.

Finally, the GBAS should have less frequent and less costly flight inspection

requirements than the ILS because the role of flight inspection for GBAS is different.

Traditional flight inspection, if needed at all, primarily would apply only during the initial

installation and ground station commissioning. This flight inspection would verify the

suitability of the various approach path (FAS) definitions and ensure that the GBAS-to-

runway geometry definitions are correct. Because verifying the coverage of the VDB

data link principally is a continuity of service issue rather than an accuracy or integrity

issue, it typically would not require periodic inspection.

GBAS systems capable of supporting Category II and III operations internationally are

envisioned. Airborne system elements that would be necessary for the enhanced GLS

capability (e.g., MMR and GLS automatic landing provisions) already are well on the way to

certification or operational authorisation. Airborne systems and flight deck displays eventually

will evolve to take full advantage of the linear characteristic of the GLS over the angular

aspects of the ILS.

iv. GLS Operations in the US

Flight-test and operational experience with the GLS has been excellent. Many GLS-guided

approaches and landings have been conducted successfully at a variety of airports and under

various runway conditions.

Both automatic landings and landings using head-up displays have been accomplished safely

through landing rollout, in both routine and non-normal conditions.

On the pilot‘s flight displays, the GLS has been unusually steady and smooth when compared

with the current ILS systems even when critical areas necessary for the ILS approaches were

unprotected during the GLS approaches.

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4 THE PERFORMANCE BASED NAVIGATION CONCEPT

4.1 Description of Performance Based Navigation

4.1.1 Introduction

The continuing growth of aviation places increased demands on airspace capacity thereby

emphasising the need for optimum utilisation of available airspace. Improved operational efficiency

derived from the application of area navigation (RNAV) has resulted in the development of different

RNAV applications in various regions of the world and for all phases of flight. These airborne

applications could potentially be expanded to provide guidance for ground movement operations.

RNAV systems evolved in a manner similar to air routes and procedures based on conventional

ground-based NAVAIDS. Historically a specific RNAV system would be identified and its performance

would then be evaluated through a combination of analysis and flight testing. For domestic

operations, the initial RNAV systems used VOR and DME as navigation signal source to calculate

position, for oceanic operations various types of inertial navigation systems (INS) were employed.

These ―new‖ systems were each developed, evaluated and certified separately. Airspace and

obstacle clearance criteria were developed based on the performance of the available equipment. In

some cases, the individual model and make of equipment that could be operated within the airspace

concerned was specifically identified. Such prescriptive requirements resulted in delays to the

introduction of new RNAV system capabilities and higher costs for maintaining appropriate

certification. To avoid such prescriptive requirements, the ICAO developed an alternative method for

defining equipage requirements by specifying the performance requirements. This is termed

Performance-Based Navigation (PBN).

Requirements for navigation applications on specific routes or within a specific airspace must be

defined and regulated in a clear and concise manner by the appropriate authority. This will enable

compliance by air operators with specific airspace requirements, including navigation specifications

that must be developed to allow the maximum benefit possible by the wide spread application of

RNAV procedures.

a. General.

The PBN concept specifies that aircraft RNAV system performance requirements be defined

in terms of accuracy, integrity, availability, continuity and functionality required for the

proposed operations in the context of a particular airspace concept, when supported by the

appropriate navigation infrastructure. The PBN concept represents a shift from sensor-based

to Performance-Based Navigation. Performance requirements are identified in navigation

specifications, which also identify the choice of navigation sensors and equipment that may

be used to meet the performance requirements. The ICAO defined navigation specifications

provide specific implementation guidance for States and operators in order to facilitate global

harmonization.

The PBN concept suggests that during PBN implementation the first step would be to define

and then publish generic navigation requirements based on specific operational requirements.

Operators then evaluate equipment options in respect of available technology and navigation

infrastructure. The operator is thus free to select the most cost-effective option in terms of

equipment to meet the published requirements for operation in a particular airspace.

Technology can evolve over time without requiring published procedures to be revisited,

provided that the required navigation performance is provided by the RNAV system (or RNP

system).

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b. Benefits.

PBN offers a number of advantages over the sensor-specific method of airspace and

procedure design. For instance, PBN:

i. reduces the need to maintain sensor-specific routes and procedures, and their associated

costs. For example, moving a single VOR ground facility can impact dozens of

procedures, VOR approaches, missed approaches, etc. Adding new sensor-specific

procedures will compound this cost, and the rapid growth in available navigation systems

would soon make sensor-specific routes and procedures unaffordable;

ii. avoids the need for development of sensor-specific operations with each new evolution of

navigation systems, which would be cost-prohibitive. The expansion of GNSS is expected

to contribute to the continued diversity of RNAV systems in different aircraft. The original

basic GNSS equipment is evolving due to the development of augmentations such as

SBAS, GBAS and GRAS, while the introduction of Galileo and the modernisation of GPS

and GLONASS will further improve GNSS performance. The use of GNSS/inertial

integration is also expanding;

iii. allows for more efficient use of airspace (route placement, fuel efficiency, noise

abatement, etc.);

iv. clarifies the way in which RNAV systems are used; and

v. facilitates the operational approval process for operators by providing a limited set of

navigation specifications intended for global use.

c. Context of PBN.

PBN is one of several enablers of an airspace concept. Communications, ATS surveillance

and ATM are also essential elements of an airspace concept. The concept of PBN relies on

the use of RNAV systems. There are two core input components for the application of PBN:

i. The NAVAID

infrastructure;

ii. The navigation

specification;

Applying the above

components in the context

of the airspace concept to

ATS routes and instrument

procedures results in a

third component:

iii. The navigation application.

d. Scope of Performance Based Navigation.

i. Lateral Performance

For legacy reasons associated with the previous RNP concept, PBN is currently limited to

operations with linear lateral performance requirements and time constraints. For this reason,

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operations with angular lateral performance requirements (i.e. approach and landing

operations with vertical guidance for APV-I and APV-II GNSS performance levels, as well as

ILS/MLS/GLS precision approach and landing operations) are not yet addressed by the ICAO.

Linear vs. Angular Guidance

Note: — While at present the PBN manual does not provide any navigation specification

defining longitudinal flight technical error - FTE (i.e. required time of arrival or 4D control), the

accuracy requirement of RNAV and RNP specifications are defined for the lateral and

longitudinal dimensions, thereby enabling future navigation specifications defining FTE to be

developed

ii. Vertical Performance

Unlike the lateral monitoring and obstacle clearance, for barometric VNAV operations (as

discussed under All Weather Operations, Sensor Specific Area Navigation Procedures) there

is neither alerting on vertical position error nor is there a two-times relationship between a 95

per cent required total system accuracy and the performance limit. Therefore, barometric

VNAV is not considered as vertical RNP.

4.1.2 Navigation Specification

A navigation specification is used by a State as the basis for the development of airworthiness

and operational approval requirements. The navigation specification details the performance

required of the RNAV system in terms of accuracy, integrity, availability and continuity, what

navigation functionalities the RNAV system must have, which navigation sensors must be

integrated into the RNAV system and what requirements are placed on the flight crew. The

ICAO navigation specifications are contained in PBN Manual Doc 9813 Volume II.

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A navigation specification

is either a RNP

specification or a RNAV

specification. A RNP

specification includes a

requirement for on-board

self-contained

performance monitoring

and alerting, while a RNAV

specification does not.

a. On-board Performance Monitoring and Alerting.

On-board performance monitoring and alerting is the main element that determines if the

RNAV system complies with the safety level associated with a particular RNP application.

This relates to both lateral and longitudinal navigation performance and it allows the aircrew

to monitor the navigation performance against the required standard for the operation.

RNP systems provide improvements on the integrity of operation and this may permit closer

route spacing in a specific airspaces. The use of RNP systems may therefore offer significant

safety, operational and efficiency benefits.

On-board means that the performance monitoring and alerting is affected on board the

aircraft, the monitoring

and alerting relates to:

Flight technical error

(FTE)

Navigation system

error (NSE)

Path definition error

(PDE) which is

considered

negligible.

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Containment refers to the region within which the aircraft will remain 95% of the time. The

associated terms have been ―containment value‖ and ―containment distance‖ and the related

airspace protection on either side of a RNAV ATS route.

Containment Limits

Monitoring refers to the functional requirements of the aircraft‘s navigation system

performance with regard to its ability to determine positioning error and or to follow the

desired path.

Alerting relates to the crew being informed if the aircraft‘s navigation system fails to perform

to the required standard.

RNP Monitoring and Alerting

b. Navigation Functional Requirements.

Navigation system functional requirements are defined to demand either a RNAV system or A

RNP system. Both the RNAV system and RNP system specifications include requirements for

certain navigation functionalities. At the basic level, these functional requirements are:

Continuous indication of aircraft position relative to track to be displayed to the pilot flying

on a navigation display,

The display must be situated in the primary field of view of the pilot flying;

A display of distance and bearing to the active (To) waypoint;

A display of ground speed or time to the active (To) waypoint;

A navigation data storage function; and

An appropriate failure indication of the RNAV system, including the sensors.

More sophisticated navigation specifications include the requirement for navigation databases

(see section 1.2.2) and the capability to execute database procedures.

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c. Designation of RNP and RNAV Specifications.

Designation of RNP and RNAV expressed by the letter ―X‖ denotes the lateral navigation

accuracy in nautical miles, which is expected to be achieved at least 95% of the flight time by

aircraft operating in a particular airspace, or on a particular procedure or route. The navigation

specification designation is the abbreviated title for the navigation system (RNAV or RNP

system – see note below) performance and functionality requirements.

Note: — Here we are referring to the RNAV system and RNP system as understood under

the new PBN concept. The fundamental difference being that an RNP system shall

include onboard monitoring and alerting where as an RNAV system does not

include this functionality.

i. RNP Specification.

A navigation specification based on RNAV that includes the requirement for performance

monitoring and alerting. RNP specifications are designated by the prefix RNP followed by the

numerical value of the navigation accuracy for the intended operation e.g. RNP 4.

ii. RNAV Specification.

A navigation specification based on RNAV that does not include the requirement for

performance monitoring and alerting. RNAV specifications are designated by the prefix RNAV

followed by the numerical value of the navigation accuracy for the intended operation e.g.

RNAV 5.

Approach navigation specifications cover all segments of the instrument approach procedure

from the arrival to the missed approach. The designation for approach is expressed by the

prefix RNP only and is followed by an abbreviated suffix e.g. RNP APCH or RNP AR APCH.

Due to the definitive nature of navigation specifications, an aircraft approved for stringent

accuracy requirement e.g. a RNP specification is not automatically approved for a less

stringent accuracy RNAV specification. This is due to the difference is in the functional

requirements for each navigation specification and therefore aircraft approved for a more

stringent accuracy requirement may not necessarily meet the functional requirements for a

less stringent accuracy requirement.

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d. RNP Concept vs. RNAV.

i. Oceanic, Remote Continental, En-Route and Terminal Operations

For oceanic, remote continental, en-route and terminal operations, a RNP specification is

designated as RNP X, e.g. RNP 4. A RNAV specification is designated as RNAV X, e.g.

RNAV 1. If two navigation specifications share the same value for X, they may be

distinguished by use of a prefix, e.g. Advanced-RNP 1 and Basic-RNP 1.

For both RNP and RNAV designations, the expression ―X‖ (where stated) refers to the lateral

navigation accuracy in nautical miles, which is expected to be achieved at least 95 per cent of

the flight time by the population of aircraft operating within the airspace, route or procedure.

ii. Approach

Approach navigation specifications cover all segments of the instrument approach. RNP

specifications are designated using RNP as a prefix and an abbreviated textual suffix, e.g.

RNP APCH or RNP AR APCH. There are no RNAV approach specifications.

(1) PBN Procedures

(2) Basic-RNP 1

(3) Advanced - RNP 1 (Future development)

(4) RNP 2 (Future development)

(5) RNP APCH

(6) RNP AR APCH

iii. Understanding RNAV and RNP Designations

In cases where navigation accuracy is used as part of the designation of a navigation

specification, it should be noted that navigation accuracy is only one of the many performance

requirements included in a navigation specification.

Because specific performance requirements are defined for each navigation specification, an

aircraft approved for RNP specifications is not automatically approved for all RNAV

specifications. Similarly, an aircraft approved for RNP or RNAV specification having a

stringent accuracy requirement (e.g. RNP 0.3 specification) is not automatically approved for

a navigation specification having a less stringent accuracy requirement (e.g. RNP 4).

It may seem logical, for example, that an aircraft approved for Basic-RNP 1 be automatically

approved for RNP 4, however, this is not the case. Aircraft approved to the more stringent

accuracy requirements may not necessarily meet some of the functional requirements of the

navigation specification having a less stringent accuracy requirement.

iv. Flight Planning of RNAV and RNP Designations

Manual or automated notification of an aircraft‘s qualification to operate along an ATS route,

on a procedure or in a particular portion of airspace is provided to ATC via the Flight Plan.

Flight Plan procedures are addressed in Procedures for Air Navigation Services — Air Traffic

Management (PANS-ATM) (Doc 4444).

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v. Accommodating Inconsistent RNP Designations

The existing RNP 10 designation is inconsistent with PBN RNP and RNAV specifications.

RNP 10 does not include requirements for on-board performance monitoring and alerting. For

purposes of consistency with the PBN concept, RNP 10 is referred to as RNAV 10 in this

manual. Renaming current RNP 10 routes, operational approvals, etc., to a RNAV 10

designation would be an extensive and expensive task, which is not cost-effective.

Consequently, any existing or new operational approvals will continue to be designated RNP

10, and any charting annotations will be depicted as RNP 10 (see graphic below).

Accommodating existing and future designations

In the past, the United States and member States of the European Civil Aviation Conference

(ECAC) used regional RNAV specifications with different designators. The ECAC applications

(P-RNAV and B-RNAV) will continue to be used only within those States. Over time, ECAC

RNAV applications will migrate towards the international navigation specifications of RNAV 1

and RNAV 5. The United States migrated from the US RNAV Types A and B to the RNAV 1

specification in March 2007.

vi. Minimum Navigation Performance Specification (MNPS)

Aircraft operating in the North Atlantic airspace are required to meet a minimum navigation

performance specification (MNPS). The MNPS has intentionally been excluded from the

above designation scheme because of its mandatory nature and because future MNPS

implementations are not envisaged. The requirements for MNPS are set out in the

Consolidated Guidance and Information Material concerning Air Navigation in the North

Atlantic Region (NAT Doc 001).

vii. Future RNP Designations

It is possible that RNP specifications for future airspace concepts may require additional

functionality without changing the navigation accuracy requirement. Examples of such future

navigation specifications may include requirements for vertical RNP and time-based (4D)

capabilities. The designation of such specifications will need to be addressed in future

developments of the ICAO PBN manual.

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4.1.3 NAVAID Infrastructure

NAVAID Infrastructure comprises the NAVAIDs that support or provide the position

capabilities and is referred to as ground- or space-based NAVAIDS. NAVAIDS are

categorised as follows:

Ground-based NAVAIDs include DME and VOR, or

Space-based NAVAIDs include GNSS elements.

4.1.4 Navigation Application

This is the application of a navigation specification and associated NAVAID infrastructure to

ATS routes, instrument approach procedures and/or defined airspace volume in accordance

with the airspace concept, i.e. the concept of matching the navigation specification against the

navigation aid infrastructure. Navigation application includes RNAV or RNP SIDs and STARs,

RNAV or RNP ATS routes and RNP approach procedures. The designator of a Navigation

Application matches the corresponding Navigation Specification, i.e.

A RNP application is supported by RNP specifications, and

A RNAV application is supported by RNAV specifications.

Navigation Applications indicating the designation of the required Navigation Specification

plus any established limitation imposed for the particular Navigation Application will be

outlined on the relevant instrument procedure charts and AIPs.

Application of navigation specification by flight phase:

Navigation

Specification

Flight Phase

En-route

Oceanic/remote

En-route

Continental

Arrival

Approach

Departure Initial Intermediate Final Missed

RNAV 10 10

RNAV 5 5 5

RNAV 2 2 2 2

RNAV 1 1 1 1b 1

RNP4 4

Basic-RNP1 1a,c 1a 1a 1a,b 1a,c

RNPAPCH 1 1 0.3 1

a. The navigation application is limited to use on STARs and SIDs only.

b. The area of application can only be used after the initial climb of a missed approach phase.

c. Beyond 30 NM from the airport reference point (ARP), the accuracy value for alerting becomes 2 NM.

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4.1.5 Future Developments

Under PBN, Navigation Applications will progress from 2D to 3D/4D. Consequently, on-board

performance monitoring and alerting is still to be developed in the vertical plane (vertical

RNP) and ongoing work is aimed at harmonising longitudinal and linear performance

requirements. It is also possible that angular performance requirements associated with

approach and landing may be included in the scope of PBN in the future. Similarly,

specifications to support helicopter-specific navigation applications and holding functional

requirements may also be included.

Operators are preparing for the application of trajectory-based operations (TBO), i.e. 3D and

4D RNAV operations. TBO presents lateral and vertical flight profile for aircraft that are

specific, but highly flexible and adaptable to operational needs. These types of operations

allow for ―real time‖ flight profile changes depending on the navigation accuracy required. This

type of operation also allows for the definition of climb and descent points as well as time of

arrival definition to meet the prevailing ATS requirement. The availability of this level of

navigation capability from takeoff to landing will ensure navigation accuracy along a route,

procedure or airspace both laterally and vertically.

As more reliance is placed on GNSS, the development of airspace concepts will increasingly

need to ensure the coherent integration of navigation, communication and ATS surveillance

enablers. Future ATM developments will allow different States to employ the most cost

effective and relevant navigation specifications. See the following example;

An example of different States employing different NAVAID solutions

to achieve a similar result.

The RNAV 1 specification in Volume II of this manual shows that any of the following

navigation sensors can meet its performance requirements: GNSS or DME/DME/IRU or

DME/DME. Sensors needed to satisfy the performance requirements for a RNAV 1

specification in a particular State are not only dependent on the aircraft on-board capability.

A limited DME infrastructure or GNSS policy considerations may lead the authorities to

impose specific navigation sensor requirements for a RNAV 1 specification in that State. As

such, State A‘s AIP could stipulate GNSS as a requirement for its RNAV 1 specification

because State A only has GNSS available in its navaid infrastructure. State B‘s AIP could

require DME/DME/IRU for its RNAV 1 specification (policy decision to not allow GNSS).

Each of these navigation specifications would be implemented as a RNAV 1 application.

However, aircraft equipped only with GNSS and approved for the RNAV 1 specification in

State A would not be approved to operate in State B.

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a. Merge Point Procedure.

A Merge Point Procedure is a published instrument procedure that is designed to make full

use of the capability of the airborne navigation systems available today. This is achieved by

requiring and aircraft to follow a published route to final approach, whilst complying with

height/level, speed and time restrictions and with minimal or no ATC intervention (i.e. no

vectoring and minimal talking). This type of procedure is in use today at a number of the

major European airports, Paris, Frankfurt and Brussels to name a few. Let‘s see how this is

possible and we will start by defining a few terms.

i. Point Merge System

A ―Point Merge system‖ forms part of a route structure, enabling the integration of two or more

inbound flows into one

sequence and is

characterised by the

features described below.

ii. Merge point

Traffic integration at a

merge point is achieved by

merging inbound flows to a

single point. After this

merge point, aircraft are

established on a fixed

common route until the exit

of the Point Merge system.

iii. Sequencing legs

Before the merge point, a ‗sequencing leg‘ is dedicated to path stretching/shortening for each

inbound flow. While along a sequencing leg, aircraft can be instructed to fly ‗Direct To‘ the

merge point at any appropriate time (i.e. be kept for a certain amount of time on the leg for

path stretching, or inversely sent early direct to the merge point for path shortening).

Sequencing legs have a pre-defined maximum length at ‗iso-distance‘ from the merge point

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1

In order for the controller to easily and intuitively determine the appropriate moment to issue

the ‗Direct-To‘ instructions for each aircraft, based on its spacing with the preceding aircraft in

the sequence, and without requiring the support of any new ground tool, the geometry of the

Point Merge System shall ensure that:

aircraft left flying on a sequencing leg are kept (approximately) at the same distance

(‗iso-distance‘) from the merge point all along this leg (this requirement has an impact on

the shape of the sequencing legs, which shall be as close as possible to arcs of circle),

and

distinct sequencing legs are (approximately) located at the same distance from the

merge point.

(1) Example

Shown here is a typical Point Merge System depicting a simple configuration with two

inbound flows.

This Point Merge System is composed of two sequencing legs that are:

parallel, flown in opposite directions and are vertically separated;

segmented, forming quasi-arcs centred on the merge point (iso-distance

requirement).

The resulting envelope of possible paths towards the merge point forms a ―triangle-

shaped‖ area.

Notes:

(1) Aircraft enter the Point Merge System upon reaching a defined waypoint which will

generally be located ahead of the sequencing leg‘s entry.

(2) Aircraft leave the Point Merge System upon reaching a defined waypoint which will

generally be located after the merge point.

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At this stage, it shall be remarked

that the Point Merge procedure is

not thought of as an open-ended

STAR. It should be designed so

that if the aircraft reaches the end

of the sequencing leg without

receiving a ‗Direct To‘ clearance

(which is not expected to occur

under nominal circumstances), it

turns automatically towards the

merge point as shown in the

diagram adjacent.

In the rest of the document, we will

always consider the Point Merge

procedure as being (part of) a

closed STAR. However, for the sake of readability, the figures in this document will generally

not include the ‗closing part‘ of the Point Merge procedure.

iv. Variants

There is actually a wide range of possible variants regarding the geometry and parameters of

a Point Merge System. Still, all these possible options are based on the same high level

principles, and are compatible with the proposed operating method. Local constraints may

impose specific design choices, conversely, some environments may offer certain flexibility in

the design of a route structure supporting Point Merge operations. In particular, the length of

the sequencing legs will directly influence the maximum extent of path stretching. One may

develop any one of a number of permutations varying from the basic Point Merge System

through to a Point Merge System with fully dissociated sequencing legs.

Shown adjacent is an example of a

Point Merge Systems dealing with

two inbound flows and comprising

two sequencing legs that are:

shorter, separate (dissociated)

and of opposite directions (left

hand side diagram) or same

direction (right hand side

diagram);

segmented, approximating

arcs of a circle centred on the

merge point (iso-distance

requirement).

v. Impact on vertical profiles

In the Merge Point Figure 1 above (parallel sequencing legs), aircraft from the outer

sequencing leg will generally cross the inner leg once instructed ‗Direct To‘ the merge point,

lateral separation between aircraft from different arrival flows is not ensured by design.

Consequently, the legs will need to be vertically separated (see Merge Point Figure 4 as an

example). Different solutions may be envisaged

ATNS/HO/C09/30/02/01 of 184 14 July 2010

one option may be to require aircraft to level off when flying along the sequencing legs.

This would be the most constraining option. However, even in that case, when leaving the

legs, the distance to go (DTG) will be known by the FMS and in case the Point Merge

System is located in such a way that aircraft entering it have already reached their top of

descent (TOD), continuous descent approaches (CDAs) will already be possible from the

level/altitude of the sequencing legs;

a second option would be to define and publish vertical restrictions that would enable

aircraft to follow a ‗gentle descent‘ along both legs (e.g. from FL130 down to FL110 on

one leg, and from FL100 to FL080 on the other one – see Merge Point Figure 5). Once

instructed to fly ‗Direct To‘ the merge point, the vertical profile can be adjusted taking into

account the updated DTG information. This will then allow for the application of the CDA

concept from earlier on in the descent or even allow for CDA from the cruise level.

In the Merge Point Figure 3 above (dissociated sequencing legs), aircraft flying the procedure

are normally expected to be separated longitudinally and/or laterally from each other.

Consequently, the vertical separation constraint is released (subject to other local

requirements) and aircraft could be in descent at all times while in the Point Merge System.

More efficient CDAs from closer to the cruise level may become possible.

vi. Separation between sequencing legs

As a general rule, the design of the route structure shall enable segregation between arrivals

from different flows (in addition to strategic de-confliction between arrivals and departures),

before the sequence is built. In particular, sequencing legs shall be appropriately separated in

the lateral and/or vertical planes.

In case of parallel sequencing legs, due consideration shall be given to the following aspects

regarding their lateral separation:

they shall not be located too far apart in the horizontal plane, so as to comply with the

requirement to be – approximately – at the same distance from the merge point, and

thus gain some precision on inter-aircraft spacing when applying the procedure. From

this perspective, it is recommended to avoid using a large lateral distance between

parallel legs (e.g. equal to, or larger than the required separation);

on the other hand, the legs should not be designed too close to each other in order to

avoid display cluttering on the controller‘s radar display.

Therefore a trade-off has to be found, e.g. sequencing legs 2nm apart (which, assuming a

3nm separation standard for instance, also requires the sequencing legs to be vertically

separated as stated above).

Regarding vertical separation between the sequencing legs, due consideration shall be

given to the following aspects:

differences in levels/altitudes used along the sequencing legs shall not be too large; this

is due to the need to keep aircraft at compatible speeds for sequence

building/maintenance, and in view of their descent for reaching the same altitude at the

merge point while ensuring longitudinal separation;

parallel sequencing legs shall on the other hand be vertically separated – e.g. each

assigned with a different published level/altitude (i.e. at least 1000ft apart), or using

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appropriate vertical restrictions; consequently, again, in that case a trade-off has to be

found.

vii. Altitude restrictions

In order to ensure that there is no inadvertent descent while aircraft are flying along the

sequencing leg, the minimum altitude for the leg should be published as an ‗at or above‘

altitude restriction (or an altitude window) at its last waypoint (see Merge Point Figure 4

below).

It is further recommended that an

appropriate altitude restriction in the

form of ‗at or above‘ or vertical

window is defined at the exit of the

Point Merge System and/or at its

merge point. This will help to

influence the vertical profile

calculations once the aircraft has

been cleared for the procedure.

In case it is considered necessary to

keep the aircraft at a specific

level/altitude when flying along the

sequencing legs (e.g. parallel legs

with levelling-off), then ‗at‘ altitude

restrictions should be defined for the start and end point of these legs. Furthermore, if the

parallel legs are of opposite direction (as shown in Merge Point Figure 4), these published

vertical restrictions will probably be required in order to minimise ACAS alerts.

In case of parallel sequencing legs, in order to mitigate the risk of an aircraft still being in

descent whilst entering the sequencing leg (and therefore allow some time for ATCO to detect

a potential level bust), it is recommended that the level restriction be published on a point

ahead of the sequencing leg, ensuring that the aircraft levels off prior to entry (as shown in

Merge Point Figure 4).

Note: —

A similar design precautions are

also required in order to minimise

ACAS alerts due to the close

location of legs start and end

points in case of opposite parallel

sequencing legs.

Merge Point Figure 5 provide

examples of published altitude

restrictions for a Point Merge

System in Approach airspace, in

case of close parallel sequencing

legs with level-offs, parallel legs

with ‗gentle descent‘, or

dissociated sequencing legs. In

this example, the aircraft are

required to level off along the

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parallel sequencing legs so as to ensure vertical separation. ‗At‘ vertical restrictions are

published at the start and end points of the legs.

In Merge Point Figure 6, vertical

restrictions are set on the parallel

legs so that aircraft from IAF1 will

remain below aircraft from IAF2

while along the legs. In both cases

however, they may follow a ‗gentle

descent‘. Such design may provide

a seamless transition between:

situations where traffic load

still enables to follow an

efficient vertical path (aircraft

do not fly a long distance

along the sequencing legs

and do not need to level off),

and

situations where the traffic load is such that the need to achieve a safe and efficient

runway sequence does not allow anymore the systematic optimisation of individual

vertical profiles (aircraft fly longer distances along the legs and reach a point where they

may need to level off).

In Merge Point Figure 7, legs are

dissociated and aircraft from IAF1

and from IAF2 may follow

independently optimised vertical

profiles. There is an uncertainty on

the ‗distance to go‘ until aircraft turn

Direct To the merge point, at which

time the aircrew can adjust the rate

of descent according to the actual

remaining distance to touchdown.

Vertical restrictions may be

published as pictured here – at the

first point of each leg so as to

ensure that aircraft turning

immediately to the merge point will

be able to descend with a shorter

DTG.

viii. Speed restrictions

Speed restrictions may also be defined at certain waypoints in a Point Merge system. For

instance, if it is the intention of ATC to reduce all aircraft to a common speed when they enter

the sequencing leg, this should be published as a speed restriction at the entry waypoint. It

may then be desirable to also publish an altitude restriction at the same waypoint to ensure

that all P-RNAV systems take account of the speed restriction.

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ix. Other charting aspects

Waypoints in a Point Merge System (including the merging point) should be fly-by waypoints,

with the exception of the last point at the end of the sequencing leg in the ‗closing part‘ of the

procedure which should be a fly-over waypoint.

The waypoint names in a Point Merge System shall conform to naming conventions such as

those published for RNAV waypoints. Waypoints on the sequencing legs could be identified

using the alphanumeric naming conventions. The merge point should be considered as a

strategic waypoint to ATC, and thus be named using 5 letter globally unique pronounceable

ICAO Name codes.

The Point Merge procedure should be detailed in the AIP, or in a supporting AIC. The charts

should not be cluttered with detailed notes about the concept apart from a note stating ‗Point

Merge procedures in operation, expect clearance direct to merge points (WPT NAMES) once

past IAF. CDA profiles to be followed once inbound to the merge point‘, or a similar

statement.

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4.2 Airspace Concept

4.2.1 Introduction

An airspace concept may be viewed as

a general vision or a master plan for a

particular airspace. Based on particular

principles, an airspace concept is

geared towards specific objectives.

Airspace concepts need to include a

certain level of detail if changes are to

be introduced within a particular portion

of airspace. Details could explain, for

example, airspace organization and

management and the roles to be

played by various stakeholders and

airspace users. Airspace concepts may

also describe the different roles and

responsibilities, mechanisms used and the relationships between people and machines.

Strategic objectives drive the general vision of the airspace concept. These objectives are usually

identified by airspace users, air traffic management (ATM), airports as well as environmental and

government policy. It is the function of the airspace concept and the concept of operations to respond

to these requirements. The strategic objectives which most commonly drive airspace concepts are

safety, capacity, efficiency, access and the environment. As Examples 1 and 2 below suggest,

strategic objectives can result in changes being introduced to the airspace concept.

Example 1

Safety: The design of RNP instrument approach procedures could be a way of

increasing safety (by reducing Controlled Flights into Terrain (CFIT).

Capacity: Planning the addition of an extra runway at an airport to increase capacity will

trigger a change to the airspace concept (new approaches to SIDs and STAR

required).

Efficiency: A user requirement to optimise flight profiles on departure and arrival could

make flights more efficient in terms of fuel burn.

Environment: Requirements for reduced emissions, noise preferential routes or continuous

descent arrivals/approaches (CDA), are environmental motivators for change.

Access: A requirement to provide an approach with lower minima than supported by

conventional procedures, to ensure continued access to the airport during

bad weather, may result in the development and publication of a RNP

approach to that runway.

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Example 2

Although GNSS is associated primarily with navigation, GNSS is also the backbone of ADS-B

surveillance applications. As such, GNSS positioning and track-keeping functions are no

longer ―confined‖ to being a navigation enabler to an airspace concept. GNSS, in this case, is

also an ATS surveillance enabler. The same is true of data-link communications: data are

used by an ATS surveillance system (for example, in ADS-B and navigation).

4.2.2 The Airspace Concept

a. Airspace Concepts and Navigation Applications.

The cascade effect from strategic objectives to the airspace concept places requirements on the

various ―enablers‖ such as communication, navigation, ATS surveillance, air traffic management

and flight operations. The navigation functional requirements within a Performance-Based

Navigation context need to be identified. These navigation functionalities are formalised in a

navigation specification which, together with a navigation aid infrastructure, supports a particular

navigation application. As part of an airspace concept, navigation applications also have a

relationship to communication, ATS surveillance, ATM, ATC tools and flight operations, which are

also inherent in the airspace concept.

Relationship: Performance-Based Navigation and Airspace Concept

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4.2.3 Airspace Concepts by Area of Operation

Area of operation

a. Oceanic and Remote Continental.

Oceanic and remote continental airspace concepts are currently served by two navigation

applications, RNAV 10 and RNP 4. Both these navigation applications rely primarily on GNSS to

support the navigation element of the airspace concept. In the case of the RNAV 10 application,

no form of ATS surveillance service is required. In the case of the RNP 4 application, ADS

contract (ADS-C) is used.

Note: – RNAV10 retains the RNP10 designation.

AREA of OPERATION

NAVIGATION

APPLICATION

NAVIGATION

SPECIFICATION

NAVAID

INFRASTRUCTURE COMMUNICATION SURVEILLANCE

Oceanic En route ATS routes RNAV 10 GNSS RTF (voice) Procedural Service

Oceanic En route ATS routes RNP 4 GNSS RTF (voice)

RTF and Data links(CPDLC & ADS-C)

Procedural Service

Oceanic En route ATS routes RNAV10 IRS RTF (voice)


Procedural Service

Remote Continental

En route ATS routes RNAV 10 GNSS RTF (voice) Procedural Service

Remote Continental

En route ATS routes RNP 4 GNSS RTF (voice)


Procedural Service

Remote Continental

En route ATS routes RNAV10 IRS RTF (voice)


Procedural Service

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b. Continental En-Route.

Continental en-route airspace concepts are currently supported by RNAV applications. RNAV 5 is

used in the Middle East (MID) and European (EUR) Regions. It is designated as B-RNAV (Basic

RNAV in Europe and RNP 5 in the Middle East. In the United States, a RNAV 2 application

supports an en-route continental airspace concept. At present, continental RNAV applications

support airspace concepts which include radar surveillance and direct controller pilot

communication (voice).

AREA of OPERATION

NAVIGATION

APPLICATION

NAVIGATION

SPECIFICATION

NAVAID


Continental

En-route

En route ATS routes

RNAV 5 GNSS

DME/DME

VOR/DME

RTF (voice) ATS Surveillance Service

Continental

En-route

En route ATS routes

RNP 1 GNSS

DME/DME

RTF (voice)

Procedural Service

Continental

En-route

En route ATS routes

RNAV 2 no IRS

RNAV 1 with IRS

RNAV 1 no IRS but adequate DME

GNSS

DME/DME

RTF (voice)

Procedural Service

Continental

En-route

En route ATS routes

None available GNSS

DME/DME

RTF (voice)

Procedural Service

c. Terminal Airspace: Arrival and Departure.

Existing terminal airspace concepts, which include arrival and departure, are supported by RNAV

applications. These are currently used in the European (EUR) Region and the United States. The

European terminal airspace RNAV application is known as Precision RNAV (P-RNAV). As

indicate in the PBN Manual Doc. 9813 Volume II, although the RNAV 1 specification shares a

common navigation accuracy with P-RNAV, this regional navigation specification does not satisfy

the full requirements of the RNAV 1 specification shown in Volume II. As of the publication of this

manual, the United States terminal airspace application formerly known as US RNAV Type B has

been aligned with the PBN concept and is now called RNAV 1. Basic-RNP 1 has been developed

primarily for application in non-radar, low-density terminal airspace. In future, more RNP

applications are expected to be developed for both en-route and terminal airspace.

AREA of OPERATION

NAVIGATION

APPLICATION

NAVIGATION

SPECIFICATION

NAVAID


Terminal SIDs and STARS

RNAV 2 no IRS

RNAV 1 with IRS

RNAV 1 no IRS but adequate DME

GNSS

DME/DME

RTF (voice)

ATS Surveillance Service


Basic - RNP 1 GNSS

RTF (voice)

Procedural Service


Basic - RNP 1

RNAV 1 with GNSS only

GNSS

DME/DME

RTF (voice)


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d. Approach.

Approach concepts cover all segments of the instrument approach, i.e. initial, intermediate, final

and missed approach. They will increasingly call for RNP specifications requiring a navigation

accuracy of 0.3 NM to 0.1 NM or lower. Typically, three sorts of RNP applications are

characteristic of this phase of flight: new procedures to runways never served by an instrument

procedure, procedures either replacing or serving as backup to existing instrument procedures

based on different technologies, and procedures developed to enhance airport access in

demanding environments. The relevant RNP specifications covered in the PBN Manual Doc. 9813

Volume II are RNP APCH and RNP AR APCH.

AREA of OPERATION

NAVIGATION

APPLICATION

NAVIGATION

SPECIFICATION

NAVAID


Approach Approach RNP APCH GNSS

RTF (voice)


Approach Approach RNP APCH GNSS

RTF (voice)

Procedural* Service

Approach Approach RNP AR APCH GNSS

RTF (voice)

Procedural ** Service

Approach Approach RNP AR APCH GNSS

RTF (voice)

ATS ** Surveillance Service

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4.3 Stakeholder Uses of Performance Based Navigation

4.3.1 Introduction

Various stakeholders are involved in the development of the airspace concept and the

resulting navigation applications. These stakeholders are;

airspace planners,

procedure designers,

aircraft manufacturers,

pilots and air traffic controllers.

Each stakeholder has a different role and set of responsibilities.

Stakeholder involvement in PBN concept implementation is at;

Strategic Level: Airspace planners and procedure designers translate the PBN concept

into reality of route spacing, aircraft separation minima and procedure design.

Strategic Level: Airworthiness and regulatory authorities ensure that aircraft and crew

meet the operating requirements of the intended implementation.

Tactical Level: Controllers and pilot using PBN concept in real-time operations

Each stakeholder will focus on a particular section of the PBN concept that is in line with their

line of operation.

PBN elements and specific points of interest of various stakeholders

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4.3.2 Airspace Planning

The two major elements of airspace planning are determination of separation minima to be

applied and route spacing for use by aircraft. The Manual on Airspace Planning Methodology

for the Determination of separation Minima (Doc 9689) is a key reference document planners

should consult.

Separation minima and route spacing can generally be described as being a function of three

factors:

Navigation performance based on the PBN concept.

Aircraft‘s exposure to risk i.e. the route configuration, traffic density and operational

error.

The mitigation measures which are available to reduce risk i.e. communication,

surveillance which also include ATC procedures and other necessary tools.

Generic model used to determine separation and ATS route spacing

Aircraft-to-aircraft separation and ATS route spacing are not exactly the same. As such, the

degree of complexity of the ―equation‖ depicted graphically in the figures above depends on

whether separation between two aircraft or route spacing criteria is being determined.

Aircraft-to-aircraft separation, for example, is usually applied between two aircraft and as a

consequence, the traffic density part of the risk is usually considered to be a single aircraft

pair.

For route spacing purposes, this is not the case: the traffic density is determined by the

volume of air traffic operating along the spaced ATS routes. This means that if aircraft in

a particular portion of airspace are all capable of the same navigation performance, one

could expect the separation minima between a single aircraft pair to be less than the

spacing required for parallel ATS routes.

The complexity of determining route spacing and separation minima is affected by the

availability of an ATS surveillance service and the type of communication used. If an

ATS surveillance service is available, this means that the risk can be mitigated by

including requirements for ATC intervention.

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a. Impact of PBN on airspace planning.

When separation minima and route spacing are determined using a conventional sensor-

based approach, the navigation performance data used to determine the separation minima

or route spacing depend on the accuracy of the raw data from specific navigation aids such

as VOR, DME or NDB. In contrast, PBN requires a RNAV system that integrates raw

navigation data to provide a positioning and navigation solution. In determining separation

minima and route spacing in a PBN context, this integrated navigation performance ―output‖ is

used.

It needs to be remembered that the navigation performance required from the RNAV system

is part of the navigation specification. To determine separation minima and route spacing,

airspace planners fully exploit that part of the navigation specification which prescribes the

performance required from the RNAV system. Airspace planners also make use of the

required performance, namely, accuracy, integrity, availability and continuity to determine

route spacing and separation minima.

RNAV specifications and RNP specifications are applied in this process. It is expected, for

example, that the separation minima and route spacing derived from a RNP 1 specification

will be smaller than those derived from a RNAV 1 specification, though the extent of this

improvement has yet to be assessed.

In procedurally controlled airspace, separation minima and route spacing based on RNP

specifications are expected to provide a greater benefit than those based on RNAV

specifications. This is because the on-board performance monitoring and alerting function

could alleviate the absence of ATS surveillance service by providing an alternative means of

risk mitigation.

4.3.3 Instrument Flight Procedure Design

Instrument flight procedure design includes the construction of routes, which include arrivals,

departures and approach procedures. These procedures consist of a series of predetermined

manoeuvres to be conducted solely by reference to flight instruments with specified protection

from obstacles.

States are responsible for ensuring that all published instrument flight procedures in their

airspace can be flown safely by the relevant aircraft. Safety is not only accomplished by

application of the technical criteria in the PANS-OPS (Doc 8168) and associated provisions,

but also requires measures that control the quality of the process used to apply that criteria,

which may include;

regulation,

air traffic monitoring,

ground validation and flight validation.

These measures must ensure the quality and safety of the procedure design product through

review, verification, coordination, and validation at appropriate points in the process, so that

corrections can be made at the earliest opportunity in the process.

The following paragraphs regarding instrument flight procedure design describe conventional

procedure design and sensor-dependent RNAV procedure design, their disadvantages and

the issues that led up to PBN.

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a. Non-RNAV conventional instrument flight procedure design.

Conventional procedure design is applicable to non-RNAV applications when aircraft are

navigating based on direct signals from ground-based radio navigation aids. The

disadvantage to this type of navigation is that the routes are dependent on the location of the

navigation beacons (see diagram below). This often results in longer routes since optimal

arrival and departure routes are impracticable due to siting and cost constraints on installing

ground-based radio navigation aids. Additionally, obstacle protection areas are comparatively

large and the navigation system error increases as a function of the aircraft‘s distance from

the navigation aid.

Conventional instrument flight procedure design

b. RNAV Procedures design.

Initially, RNAV was introduced using sensor-specific design criteria. A fundamental

breakthrough with RNAV was the creation of fixes defined by name, latitude and longitude.

RNAV fixes allowed the design of routes to be less dependent on the location of NAVAIDS,

therefore, the designs could better accommodate airspace planning requirements (see

graphic on the next page). The flexibility in route design varied by the specific radio navigation

system involved, such as DME/VOR or GNSS. Additional benefits included the ability to store

the routes in a navigation database, reducing pilot workload and resulting in more consistent

flying of the nominal track as compared to cases where the non-RNAV procedure design was

based on heading, timing or DME arcs. As RNAV navigation is accomplished using an aircraft

navigation computer using data from a navigation database, a major change for the designer

is the increased need for quality assurance in the procedure design process.

RNAV had a number of issues and characteristics that needed to be considered. Among

these were the sometimes wide variations in flight performance and flight paths of aircraft, as

well as the inability to predict the behaviour of navigation computers in all situations. This

resulted in large obstacle assessment areas, and, as a consequence, not much benefit was

achieved in terms of reducing the obstacle protection area.

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RNAV procedure design

As experience in RNAV operations grew, other important differences and characteristics were

discovered. Aircraft RNAV equipment, functionalities and system configurations ranged from

the simple to the complex. There was no guidance for the designer as to what criteria to apply

for the aircraft fleet for which the instrument flight procedures are being designed. Some of

the system behaviour was the result of the development of RNAV systems that would fly

database procedures derived from ATC instructions. This attempt to mimic ATC instructions

resulted in many ways to describe and define an aircraft flight path, resulting in an observed

variety of flight performance. Furthermore, the progress in aircraft and navigation technology

caused an array of types of procedures, each of which require different equipment, imposing

unnecessary costs on the air operators.

c. RNP Procedures design.

RNP procedures were introduced in the PANS-OPS (Doc 8168), which became applicable in

1998. These RNP procedures were the predecessor of the current PBN concept, whereby the

performance for operation on the route is defined, in lieu of simply identifying a required radio

navigation system. However, due to the insufficient description of the navigation performance

and operational requirements, there was little perceived difference between RNAV and RNP.

In addition, the inclusion of conventional flight elements such as flyover procedures, variability

in flight paths and added airspace buffer, resulted in no significant advantages being achieved

in designs. As a result, there was a lack of benefits to the user-community and little or no

implementation.

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d. PBN Procedures design.

Area navigation using PBN is a performance-based operation in which the navigation

performance characteristics of the aircraft are well specified and the problems described

above for the original RNAV and RNP criteria can be resolved. The performance-based

descriptions address various aircraft characteristics that were causing variations in flight

trajectories, leading to more repeatable, reliable and predictable flight tracking, as well as

smaller obstacle assessment areas. Examples of RNP APPROACH (RNP APCH) and RNP

AUTHORISATION REQUIRED APPROACH (RNP AR APCH) are shown in the figures below.

Examples of RNP APCH (left) and RNP AR APCH (right) procedures design

Note: — The fundamental advantage of the RNP AR APCH over the RNP APCH is the fact

that AR procedures may be designed to allow operations closer to obstructions

(most often high ground) and thus increase access to obstacle rich aerodrome

environments.

The main change for the designers will be that they will not be designing for a specific sensor

but according to a navigation specification (e.g. RNAV 1). The selection of the appropriate

navigation specification is based on the airspace requirements, the available NAVAID

infrastructure, and the equipage and operational capability of aircraft expected to use the

route. For example, where an airspace requirement is for RNAV-1 or RNAV-2, the available

navigation infrastructure would have to be basic GNSS or DME/DME, and aircraft would be

required to utilise either to conduct operations. Volume II of the ICAO PBN Manual (ICAO Doc

9613) provides a more explicit and complete navigation specification for the aircraft and

operator as compared to PANS-OPS (Doc 8168), Volume I. The procedure design along with

qualified aircraft and operators result in greater reliability, repeatability and predictability of the

aircraft flight path. It should be understood that no matter what infrastructure is provided, the

designer may still apply the same general design rules in fix and path placement; however,

adjustments may be required based upon the associated obstacle clearance or separation

criteria.

Integration of the aircraft and operational criteria will enable procedure design criteria to be

updated. A first effort to create such criteria is for the RNP AR APCH navigation specification.

In this case, the design criteria take full account of the aircraft capabilities and are fully

integrated with the aircraft approval and qualification requirements. The tightly integrated

relationship between aircraft, operational and procedure design criteria for RNP AR APCH

requires closer examination of aircraft qualification and operator approval, since special

authorisation is required. This additional requirement will incur cost to the airlines and will

make these types of procedures only cost beneficial in cases where other procedure design

criteria and solutions will not fit.

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4.3.4 Airworthiness and Operational Approval

Aircraft should be equipped with a RNAV system able to support the desired navigation

application. The RNAV system and aircraft operations must be compliant with regulatory

material (still to developed and published for South Africa) that reflects the navigation

specification (not yet defined for South Africa) developed for a particular navigation

application as stated in PBN Manual Doc. 9813 Volume II and approved by the appropriate

regulatory authority for the operation.

The navigation specification details the flight crew and aircraft requirements needed to

support the navigation application. This specification includes the level of navigation

performance, functional capabilities, and operational considerations required for the RNAV

system. The RNAV system installation should be certified in accordance with the ICAO Annex

8 — Airworthiness of Aircraft and operational procedures should respect the applicable

aircraft flight manual limitations, if any.

The RNAV system should be operated in accordance with recommended practices described

in the ICAO Annex 6 — Operation of Aircraft and PANS-OPS (Doc 8168), Volume I. Flight

crew and/or operators should adhere to operational limitations required for the navigation

application.

All assumptions related to the navigation application are listed in the navigation specification.

Review of these assumptions is necessary when proceeding to the airworthiness and

operational approval process. Operators and flight crew are responsible for checking that the

installed RNAV system is operated in areas where the airspace concept and the NAVAID

infrastructure described in the navigation specification is fulfilled. To ease this process,

certification and/or operational documentation should clearly identify compliance with the

related navigation specification.

a. Airworthiness approval process.

The airworthiness approval process assures that each item of the RNAV equipment installed

is of a type and design appropriate to its intended function and that the installation functions

properly under foreseeable operating conditions. Additionally, the airworthiness approval

process identifies any installation limitations that need to be considered for operational

approval. Such limitations and other information relevant to the approval of the RNAV system

installation are documented in the Aircraft Flight Manual (AFM), or AFM Supplement, as

applicable. Information may also be repeated and expanded upon in other documents such

as Pilot Operating Handbooks (POH) or flight crew operating manuals. The airworthiness

approval process is well established among States of the Operators and this process refers to

the intended function of the navigation specification to be applied.

i. Approval of RNAV systems for RNAV-X operations

The RNAV system installed should be compliant with a set of basic performance

requirements as described in the navigation specification, which defines accuracy, integrity

and continuity criteria. It should also be compliant with a set of specific functional

requirements, have a navigation database, and support each specific path terminator as

required by the navigation specification.

Note: — For certain navigation applications, a navigation database may be optional.

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For a multi-sensor RNAV system, an assessment should be conducted to establish which

sensors are compliant with the performance requirement described in the navigation

specification. The navigation specification generally indicates if a single or a dual installation

is necessary to fulfil availability and/or continuity requirements. The airspace concept and

NAVAID infrastructure are key elements in deciding if a single or a dual installation is

necessary.

ii. Approval of RNP systems for RNP-X operations

The RNP system installed should be compliant with a set of basic RNP performance

requirements, as described in the navigation specification, which should include an on-board

performance monitoring and alerting function. It should also be compliant with a set of specific

functional requirements, have a navigation database, and should support each specific path

terminator as required by the navigation specification.

For a multi-sensor RNP system, an assessment should be conducted to establish sensors

which are compliant with the RNP performance requirement described in the RNP

specification.

b. Operational approval.

The aircraft must be equipped with a RNAV system enabling the flight crew to navigate in

accordance with operational criteria as defined in the navigation specification. The State of

the Operator is the authority responsible for approving flight operations. The authority must be

satisfied that operational programmes are adequate. Training programmes and operations

manuals should be evaluated.

i. General RNAV approval process

The operational approval process first assumes that the corresponding

installation/airworthiness approval has been granted. During operation, the crew should

adhere to any limitations set out in the AFM and AFM supplements. Normal procedures are

provided in the navigation specification, including detailed necessary crew action to be

conducted during pre-flight planning, prior to commencing the procedure and during the

procedure.

Abnormal procedures are provided in the navigation specification, including detailed crew

action to be conducted in case of on-board RNAV system failure and in case of system

inability to maintain the prescribed performance of the on-board monitoring and alerting

functions.

The operator should have in place a system for investigating events affecting the safety of

operations in order to determine their origin (coded procedure, accuracy problem, etc.).

The minimum equipment list (MEL) should identify the minimum equipment necessary to

satisfy the navigation application.

ii. Flight crew training

Each pilot must receive appropriate training, briefings and guidance material in order to safely

conduct an operation.

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iii. Navigation database management

Any specific requirement regarding the navigation database should be provided in the

navigation specification, particularly if the navigation database integrity is supposed to

demonstrate compliance with an established data quality assurance process, e.g. as specified

in DO 200A/EUROCAE ED 76.

c. Flight Crew and Air Traffic Operations.

Pilots and air traffic controllers are the end-users of Performance-Based Navigation, each

having their own expectations of how the use and capability of the RNAV system affects their

working methods and everyday operations.

What pilots need to know about PBN operations is whether the aircraft and flight crew are

qualified to operate in the airspace, on a procedure or along an ATS route. For their part,

controllers assume that the flight crew and aircraft are suitably qualified for PBN operations.

However, they also require a basic understanding of area navigation concepts, the

relationship between RNAV and RNP, and how their implementation affects control

procedures, separation and phraseology. As importantly, an understanding of how RNAV

systems work as well as their advantages and limitations are necessary for both controllers

and pilots.

for pilots, one of the main advantages of using a RNAV system is that the navigation

function is performed by highly accurate and sophisticated on-board equipment allowing

a reduction in cockpit workload and, in some cases, increased safety.

in controller terms, the main advantage of aircraft using a RNAV system is that ATS

routes can be straightened, as it is not necessary for routes to pass over locations

marked by conventional NAVAIDS.

another advantage is that RNAV-based arrival and departure routes can complement,

and even replace, radar vectoring, thereby reducing approach and departure controller

workload.

Consequently, parallel ATS route networks are usually a distinctive characteristic of airspace

in which RNAV and/or RNP applications are used. These parallel track systems can be

unidirectional or bidirectional and can, occasionally, cater to parallel routes requiring a

different navigation specification for operation along each route, e.g. a RNP 4 route alongside

a parallel RNP 10 route. Similarly, RNAV SIDs and STARs are featured extensively in some

terminal airspace. From an obstacle clearance perspective, the use of RNP applications may

allow or increase access to an airport in terrain-rich environments where such access was

limited or not previously possible.

Air traffic controllers sometimes assume that, where all aircraft operating in a particular

portion of airspace may be required to be approved at the same level of performance, these

aircraft will systematically provide entirely or exactly repeatable and predictable track-keeping

performance. This is not an accurate assumption because the different algorithms used in

different FMS and the different ways of coding data used in the navigation database can

affect the way an aircraft performs during turns. Exceptions are where radius to fix (RF) leg

types and/or fixed-radius transitions (FRT) are used. Experience gained in States that have

already implemented RNAV and RNP shows that such mistaken assumptions can be

corrected by adequate training in Performance-Based Navigation. ATC training in RNAV and

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RNP applications is essential before implementation so as to enhance controllers‘

understanding and confidence, and to gain ATC ―buy-in‖.

PBN implementation without adequate emphasis on controller training can have a serious

impact on any RNP or RNAV project schedule (see the Controller Training paragraphs in

each navigation specification in Volume II of the PBN Manual, Parts B and C).

i. Flight crew procedures

Flight crew procedures complement the technical contents of the navigation specification.

Flight crew procedures are usually embodied in the company operating manual. These

procedures could include, for example, that the flight crew notify ATC of contingencies (i.e.

equipment failures and/or weather conditions) that could affect the aircraft‘s ability to maintain

navigation accuracy. These procedures would also require the flight crew to state their

intentions, coordinate a plan of action and obtain a revised ATC clearance in case of

contingencies. At a regional level, established contingency procedures should be made

available so as to permit the flight crew to follow such procedures in the event that it is not

possible to notify ATC of their difficulties.

ii. ATS procedures

ATS procedures are needed for use in airspace utilising RNAV and RNP applications.

Examples include procedures to enable the use of the parallel offset on-board functionality or

to enable the transition between airspaces having different performance and functionality

requirements (i.e. different navigation specifications). Detailed planning is required to

accommodate such a transition and may be achieved as follows:

determining the specific points where the traffic will be directed as it transits from

airspace requiring a Navigation specification with less stringent performance and

functional requirements to an airspace requiring a Navigation specification having more

stringent performance and functional requirements and

coordinating efforts with relevant parties in order to obtain a regional agreement

detailing the required responsibilities.

Air traffic controllers should take appropriate action to provide increased separation and to

coordinate with other ATC units as appropriate, when informed that the flight is not able to

maintain the prescribed level of navigation performance.

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4.4 Implementation Guidance

4.4.1 Introduction to Implementation Process

The aim of this section is to provide a brief overview of the process to be followed when

implementing RNAV or RNP applications in a given region, which might comprise a State or

group of States.

a. Process Overview.

Three processes are provided to assist States in the implementation of PBN. They are used

in sequence:

Process 1 — Determine requirements.

Process 2 — Identifying the ICAO navigation specifications for implementation.

Process 3 — Planning and implementation.

i. Process 1

This outlines steps for a State or region to determine the strategic and operational

requirements for Performance-Based Navigation via an airspace concept. Fleet equipage and

CNS/ATM infrastructure in the State or region will be assessed and navigation functional

requirements will be identified.

ii. Process 2

This describes how a State or region determines whether implementation of an ICAO

navigation specification achieves the objectives of the airspace concept, provides the required

navigation functions, and can be supported by the fleet equipage and CNS/ATM infrastructure

that have been identified from Process 1. Process 2 might lead to the need to review the

airspace concept and required navigation functions identified in Process 1, to identify trade-

offs that would allow a better fit with a particular navigation specification detailed in the ICAO

PBN Manual Doc 9813 Volume II.

iii. Process 3

This provides a hands-on guide to planning and implementation, so that the navigation

requirement may be turned into an implementation reality.

b. Development of a New Navigation Specification.

The above three processes are designed to enhance the application of harmonized global

standards, and avoid proliferation of local/regional standards. Development of a new

navigation specification would be considered in those very exceptional cases, where:

a State or region has determined that it is not possible to use an existing ICAO

navigation specification to satisfy its intended airspace concept; and

it is not possible to change the elements of a proposed airspace concept so that an

existing ICAO navigation specification can be used.

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Chapter 5 of the PBN Manual provides guidance for an ICAO-coordinated development of a

new navigation specification. Such a development is an extensive and rigorous exercise in

airworthiness and flight operations development. It should be expected to be a very complex

and lengthy effort leading to a globally harmonized specification.

4.4.2 Process 1: Determine Requirements

a. Introduction.

The goal of Process 1 is to formulate an airspace concept and assess the existing fleet

equipage and CNS/ATM infrastructure, with the overall aim of identifying the navigation

functional requirements necessary to meet the airspace concept.

b. Input to Process 1.

The input to start this process is the strategic objectives and operational requirements

stemming from airspace users (i.e. military/civil, air carrier/business/general aviation, IFR/VFR

operations), and ATM requirements (e.g. airspace planners, ATC). Policy directives such as

those stemming from political decisions concerning environmental mitigation can also be

inputs.

The process should consider the needs of the airspace user community in a broad context,

i.e. IFR, VFR, military and civil aviation (e.g. air carrier, business and general aviation).

Consideration should also be given to domestic and international user requirements, as well

as airworthiness and operational approval for operators.

The overall safety, capacity and efficiency requirements of implementation should be

balanced; an analysis of all requirements, and trade-offs among competing requirements, will

need to be completed. Primary and alternate means of meeting requirements should be

considered; methods for communicating to airspace users the requirements and availability

(and outages) of services need to be identified; and detailed planning needs to be undertaken

for the transition to the new airspace concept.

c. Steps in Process 1.

i. Step 1: Formulate the airspace concept

An airspace concept is only useful if it is defined in sufficient detail so that supporting

navigation functions can be identified. The elaboration of the airspace concept is therefore

best undertaken by a multi-disciplinary team as opposed to a single specialization. This team

should be expected to be made up of air traffic controllers and airspace planners (from the

ANSP), pilots, procedure design specialists, avionics specialists, flight standards and

airworthiness regulators, and airspace users. Together, this team would develop the airspace

concept using the broad directions provided by the strategic objectives.

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(1) Factors that would be detailed include:

Airspace organisation and management (i.e. ATS route placement, SIDs/STARs,

ATC sectorisation);

Separation minima and route spacing;

Instrument approach procedure options;

How ATC is to operate the airspace;

Expected operations by flight crew; and

Airworthiness and operational approvals.

This team will focus their efforts on the following;

Airspace User Requirements

Airspace Requirements

Approach Requirements

Other Requirements

Expanded information for the team‘s consideration may be found in the PBN Manual

Doc. 9813 Volume II Attachment A.

ii. Step 2: Assessment of existing fleet capability and available NAVAID Infrastructure

Planners must understand the capability of the aircraft that will be flying in the airspace in

order to determine the type of implementation that is feasible for the users. Understanding

what is available in terms of NAVAID infrastructure is essential to determining how and if a

navigation specification can be supported. The following considerations should be taken into

account.

(1) Assessing aircraft fleet capability, and

(2) Assessing NAVAID infrastructure

It is important that implementing a RNAV application does not in itself become the cause for

installing new NAVAID infrastructure. The introduction of RNAV applications could result in

being able to move some existing NAVAIDS (e.g. DMEs may be relocated when they no

longer have to be co-located with VOR).

iii. Step 3: Assessment of the existing ATS surveillance system and communications

infrastructure and the ATM system.

An air traffic system is the sum of the CNS/ATM capabilities available. PBN is only the

navigation component of CNS/ATM. It cannot be safely and successfully implemented without

due consideration of the communication and ATS surveillance infrastructure available to

support the operation. For example, a RNAV 1 route will require different ATS route spacing

in a radar environment to that in a non-radar environment. The availability of communications

between the aircraft and air traffic service provider may impact the level of air traffic

intervention capability needed for safe operations. The following considerations should be

taken into account.

(1) ATS surveillance infrastructure

(2) Communication infrastructure

(3) ATM systems

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iv. Step 4 — Identify necessary navigation performance and functional requirements

It should be noted that the decision on the

choice of a RNAV or RNP navigation

specification as defined by the ICAO is not

only determined by aircraft performance

requirements (e.g. accuracy, integrity,

continuity, availability), but may also be

determined by the need for specific functional

requirements (e.g. leg transitions/path

terminators, parallel offset capabilities, holding

patterns, navigation databases).

The proposed navigation functional

requirements also need to consider:

the complexity of RNAV procedures

envisaged; the number of waypoints

needed to define the procedure; the

spacing between waypoints and the

need to define how a turn is executed;

and

whether the procedures envisaged aim

simply to connect with the en-route

operations and can be restricted to

operations above minimum vectoring

altitude/minimum sector altitude, or are

the procedures expected to provide

approach guidance

The next stage is Process 2, where the effort is made to identify the appropriate ICAO

navigation specification for implementation.

4.4.3 Process 2: Identifying the ICAO Navigation Specification for Implementation

a. Introduction.

The goal of Process 2 is to identify the ICAO navigation specification(s) that will support the

airspace concept and navigation functional requirements as defined in Process 1.

b. Input to Process 2.

The navigation functional requirements, fleet capability, and CNS/ATM capabilities will have

been identified in Process 1. These will provide the specific context against which the

planners will evaluate their ability to meet the requirements of a particular ICAO navigation

specification.

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c. Steps in Process 2.

i. Step 1: Review the ICAO navigation specifications in Volume II of the PBN Manual.

The first step in Process 2 is aimed at finding a potential match between the requirements

identified in Process 1 and those contained in one or more of the ICAO navigation

specifications in Volume II.

In reviewing one or more possible ICAO navigation specifications, planners will need to

consider the output of Process 1 with respect to:

(1) the ability of the existing aircraft fleet and available NAVAID infrastructure to meet

the requirements of a particular ICAO navigation specification, and

(2) the capabilities of their communications and ATS surveillance infrastructure, and

ATM system to support implementation of this particular ICAO navigation

specification.

ii. Step 2: Identify appropriate ICAO

navigation specification to apply in

the specific CNS/ATM

environment.

If planners determine that a particular

ICAO navigation specification can be

supported by the fleet equipage,

NAVAID infrastructure,

communications and ATS surveillance

and ATM capabilities available in the

State, proceed to Process 3: Planning

and implementation. If an ICAO

navigation specification cannot be

supported, continue with Process 2,

Step 3.

iii. Step 3: Identify trade-offs with

airspace concept and navigation

functional requirements (if

necessary).

This step is followed when an exact

match between a particular ICAO

navigation specification and the fleet

equipage, NAVAID infrastructure,

communications and ATS surveillance

and ATM capabilities available in the

State cannot be made. It is aimed at

changing either the airspace concept or navigation functional requirements, in order to select

an ICAO navigation specification. For example, operational requirements reflected in the

airspace concept could be reduced, or alternate means identified to achieve a similar (if not

identical) operational result.

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Planners should revisit the airspace concept and required navigation functions identified in

Process 1 to determine what trade-offs can be made, so as to implement a particular existing

ICAO navigation specification.

In most instances it will be possible to make sufficient trade-offs in the original airspace

concept or required navigation functions from Process 1 that an existing ICAO navigation

specification can then be selected. Once trade-offs have been made that will allow selection

of an ICAO navigation specification, proceed to Process 3: Planning and implementation.

However, if in the rare case that a State determines that it is impossible to make trade-offs in

its airspace concept and/or navigational functional requirements, the State would have to

develop a new navigation specification (discussed in the PBN Manual, Chapter 5, the ICAO

Doc. 9813).

4.4.4 Process 3: Planning and Implementation

a. Introduction.

The process described in this chapter is concerned with planning and implementing

Performance-Based Navigation. It follows upon completion of Process 1 and 2. See Inset for

a detailed discussion of some important considerations planners should keep in mind when

framing the implementation plan.

Inset — Implementation considerations In applying one of the ICAO navigation specifications for oceanic, remote continental and continental en-route operations as described in the PBN Manual Volume II, consideration should be given to the need for regional or multi-regional agreement. This is because connectivity and continuity with operations in adjoining airspace need to be considered to maximize benefits. For terminal and approach operations, the implementation of an ICAO navigation specification in the PBN Manual is more likely to occur on a single-State basis. Some TMAs are adjacent to national borders for which multinational coordination would likely be required. Where compliance with an ICAO navigation specification is prescribed for operation in an airspace or ATS routes, these requirements are to be indicated in the State‘s AIP. The decision to mandate a requirement for one or more ICAO RNAV or RNP specifications should only be considered after several factors have been taken into account. These include, but are not limited to:

the operational requirements of the airspace users (civil/military, IFR operations), as well as those of ANSPs;

regulatory requirements at both international and national levels;

the proportion of the aircraft population currently capable of meeting the specified requirements, and the cost to be incurred by operators that need to equip aircraft to meet the requirements of the navigation specification;

the benefits in terms of safety, capacity, improved access to airspace/airports or environment to be derived from implementing the airspace concept;

the impact on operators in terms of additional flight crew training;

the impact on flight crew in terms of workload; and

the impact on air traffic services in terms of controller workload and required facilities, (including automation and flight plan processing changes). Particular attention must be given to possible workload and efficiency impacts of operating mixed navigation environments.

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i. Step 1: Formulate safety plan.

The first step in Process 3 is the formulation of a safety plan for the PBN implementation.

Guidance for formulating a safety plan can be found in Safety Management Manual (SMM)

(ICAO Doc 9859). Depending on the nature of the implementation, this could be a State or

regional safety plan. Normally, such a plan would be developed together with an ANSP safety

bureau to the satisfaction of the regulatory authority. This safety plan details how the safety

assessment is to be accomplished for the proposed RNAV or RNP implementation.

ii. Step 2: Validate airspace concept for safety.

Validation of an airspace concept involves completing a safety assessment. From this

assessment, additional safety requirements may be identified which need to be incorporated

into the airspace concept prior to implementation.

Four validation means are traditionally used to validate an airspace concept:

airspace modelling;

fast-time simulation (FTS);

real-time simulation (RTS);

live ATC trials.

For simple airspace changes, it may be unnecessary to use all of the above validation means

for any one implementation. For complex airspace changes, however, FTS and RTS can

provide essential feedback on safety (and efficiency) issues and their use is encouraged.

Application of new navigation specifications can range from simple through major changes to

the airspace concept. All four types of validation are further discussed in the PBN Manual.

iii. Step 3: Procedure design.

A total system approach to the implementation of the airspace concept means that the

procedure design process is an integral element. Therefore, the procedure designer is a key

member of the airspace concept development team.

Procedure designers need to ensure that the procedures can be coded in ARINC 424 format.

Currently, this is one of the major challenges facing procedure designers. Many are not

familiar with neither the path & terminators used to code RNAV systems or the functional

capabilities of different RNAV systems. Many of the difficulties can be overcome, however, if

close cooperation exists between procedure designers and the data houses that provide the

coded data to the navigation database providers.

Once these procedures have been validated and flight inspected (see Steps 4 and 6), they

are published in the national AIP along with any changes to routes, holding areas, or airspace

structures.

The complexity involved in data processing for the RNAV system database means that in

most instances, a lead period of two AIRAC cycles is required (see PBN Manual Doc. 9813

Volume I Attachment B, Section 3 for more details).

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iv. Step 4: Procedure ground validation.

The development of a RNAV or RNP instrument flight procedure or ATS route follows a series

of steps from the origination of data through survey to the final publication of the procedure

and subsequent coding of it for use in an airborne navigation database. At each step of the

procedure design process, there should be quality control procedures in place to ensure that

the necessary levels of accuracy and integrity are achieved and maintained. These

procedures are detailed in PANS-OPS (Doc 8168), Volume II.

After designing the procedure and before a RNAV or RNP route or procedure is published,

PANS-OPS (Doc 8168) require that each procedure undergo a validation process. The

objective of validation is to:

(1) provide assurance that adequate obstacle clearance has been provided;

(2) verify that the navigation data to be published, as well as that used in the design of

the procedure, are correct;

(3) verify that all required infrastructure, such as runway markings, lighting, and

communications and navigation sources, are in place and operative;

(4) conduct an assessment of fly ability to determine that the procedure can be safely

flown; and

(5) evaluate the charting, required infrastructure, visibility and other operational factors.

Many of these factors can be evaluated, entirely or in part, during ground validation. Initial fly

ability checks should be conducted with software tools allowing the fly ability of the procedure

to be confirmed for a range of aircraft and in a full range of conditions (wind/temperature, etc.)

for which the procedure is designed. The verification of the fly ability of a RNAV or RNP

procedure can also include independent assessments by procedure designers and other

experts using specialised software or full-flight simulators. Fly ability tests using flight

inspection aircraft can be considered, but it must be borne in mind that this only proves that

the particular aircraft used for the test can execute the procedure correctly. This is probably

acceptable for the majority of less complex procedures. The size and speed of flight test

aircraft can seldom fully represent the performance of a fully loaded B747 or A340 and

therefore simulation is considered the most appropriate way to carry out the fly ability test.

Flight simulator tests should be conducted for those more complex procedures, such as RNP

AR APCH, when there is any indication that fly ability may be an issue. Software tools that

use digital terrain data (typically digital terrain elevation data (DTED) level 1 being required)

are available to confirm appropriate theoretical NAVAID coverage.

v. Step 5: Implementation decision.

It is usually during the various validation processes described above that it becomes evident

whether the proposed design can be implemented. The decision whether or not to go ahead

with implementation needs to be made.

Note: — If the available tools and/or quality of data used in Step 4 warrant, it may be

desirable to undertake Step 6 before a final implementation decision is taken.

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The decision on whether to go ahead with implementation or not will be based on certain

deciding factors. These include:

(1) whether the ATS route/procedure design meets air traffic and flight operations

needs;

(2) whether safety and navigation performance requirements have been satisfied;

(3) pilot and controller training requirements;

(4) whether changes to flight plan processing, automation, or AIP publications are

needed to support the implementation.

If all implementation criteria are satisfied, the project team needs to plan for execution of the

implementation, not only as regards their ―own‖ airspace and ANSP, but in cooperation with

any affected parties which may include ANSPs in an adjacent State.

vi. Step 6: Flight inspection and flight validation.

Flight inspection of NAVAIDs involves the use of test aircraft which are specially equipped to

gauge the actual coverage of the NAVAID infrastructure required to support the procedures,

arrival and departure routes designed by the procedure design specialist. Flight validation

continues the procedure validation process noted in Step 4. It is used to confirm the validity of

the terrain and obstruction data used to construct the procedure, and that the track definition

takes the aircraft to the intended aiming point, as well as the other validation factors listed in

Step 4.

Output from the above procedures may require the procedure design specialist to refine and

improve the draft procedures. The Manual on Testing of Radio Navigation Aids (ICAO Doc

8071) provides general guidance on the extent of testing and inspection normally carried out

to ensure that radio navigation systems meet the SARPs in Annex 10 — Aeronautical

Telecommunications, Volume I. PANS-OPS (ICAO Doc 8168), Volume II, Part 1, Section 2,

Chapter 4, Quality Assurance provides more detailed guidance on instrument flight procedure

validation.

vii. Step 7: ATC system integration considerations.

The new airspace concept may require changes to the ATC system interfaces and displays to

ensure controllers have the necessary information on aircraft capabilities. Considerations

arising from mixed equipage scenarios are discussed in the PBN Manual. Such changes

could include, for example:

(1) modifying the air traffic automation‘s flight data processor (FDP);

(2) making changes, if necessary, to the radar data processor (RDP);

(3) requiring changes to the ATC situation display; and

(4) requiring changes to ATC support tools.

There may be a requirement for changes to ANSP methods for issuing NOTAMS.

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viii. Step 8: Awareness and training material.

The introduction of PBN can involve considerable investment in terms of training, education

and awareness material for both flight crew and controllers. In many States, training packages

and computer-based training have been effectively used for some aspects of education and

training. The ICAO provides additional training material and seminars. Each navigation

specification in the PBN Manual, Volume II, Parts B and C addresses the education and

training appropriate for flight crew and controllers.

ix. Step 9: Establishing

operational implementation

date.

The State establishes an effective

date in accordance with the

requirements set out in the PBN

Manual, Volume I, Attachment B,

Data Processes. Experience has

identified that an additional time

period (e.g. one to two weeks)

should be allocated prior to the

operational implementation date.

This additional period is to ensure

ground and airborne system data

are properly loaded and validated in

databases.

x. Step 10: Post-implementation

review.

After the implementation of PBN,

the system needs to be monitored

to ensure that safety of the system

is maintained and to determine

whether strategic objectives have

been achieved. If after

implementation, unforeseen events

do occur, the project team should

put mitigation measures in place as

soon as possible. In exceptional circumstances, this could require the withdrawal of RNAV or

RNP operations while specific problems are addressed.

A system safety assessment should be conducted after implementation and evidence

collected to verify that the safety of the system is assured (see the Safety Management

Manual (SMM) ICAO Doc 9859).

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4.4.5 Guidelines for Development of a New Navigation Specification

a. Introduction.

In most instances, it will be possible to use an existing ICAO navigation specification from

PBN Manual Doc. 9813 Volume II to satisfy the navigation requirements for a State or

region‘s planned airspace concept. In the rare case that a State or region is not able to

complete Process 2 and select an ICAO navigation specification, the State or region would

have to develop a new navigation specification. In order to avoid proliferation of regional

standards, a new navigation specification would be subject to the ICAO review, and ultimately

be available for global application. There are guidelines in the PBN Manual that address this

situation.

Development of a new navigation specification should only be undertaken if it becomes

impossible to make acceptable trade-offs between the defined airspace concept and

navigational functional requirements that can be supported by a standard ICAO navigation

specification.

It should be recognised that development of a new navigation specification involves a

rigorous evaluation of navigation equipment and its operation. This will require even greater

involvement by airworthiness authorities than required in Process 2. While a considerable

amount of the preparatory work for development of a new navigation specification would

initially be undertaken as part of Processes 1 and 2, the State or region concerned must

undertake a full analysis at every step. Review and modifications to the work done in

Processes 1 and 2 may also need to be accomplished in whole or in part.

b. Steps for developing a new Navigation Specification.

i. Step 1: Feasibility assessment and business case.

When developing a new navigation specification, the question of the feasibility of establishing

a new navigation specification that can realistically be met by aircraft manufacturers and

operators, and achieving cost-effective implementation of that navigation specification, is

particularly important. It is necessary to undertake a feasibility assessment and to develop a

business case.

The business case assesses the benefits to be derived from the proposed airspace concept

and the cost of implementing a new navigation specification. The cost information will be

derived from the proposed functions included in the planned new navigation specification,

together with estimates of installation and certification costs.

It should be understood that the timescales from initial definition of a new requirement to

availability in new RNAV or FMS systems can be in excess of five to seven years.

Development from this point to one where the majority of the aircraft fleet operating in a given

airspace by natural (non-mandated) upgrading of the RNAV equipment can be in excess of

15 years. Thus, development of a new navigation specification normally involves using

navigation functional requirements already provided by manufacturers without the existence

of certification or operational approval.

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(1) Outline of a new navigation specification

The outline is a product of the business case and has to take due account of the functional

requirements needed to meet the airspace concept. It has to be produced with sufficient detail

to enable aircraft manufacturers to prepare cost estimates for the upgrades to RNAV systems

(including RNP systems).

ii. Step 2: Development of a navigation specification.

Contact should be made early with the ICAO in identifying the airspace concept that is to be

introduced and the foreseen need for a new navigation specification. The role of the ICAO in

this process will be to support the State or region in a detailed review of its requirements, in

order to ensure subsequent global acceptability of the new navigation specification.

Starting from the airspace concept which developers identified at the beginning of their PBN

implementation efforts, it will then be necessary to detail the requirements against which the

aircraft and its operation will ultimately be approved. In its coordinating role, the ICAO will be

able to identify other States or regions which may be in the process of developing a new

navigation specification with similar operational and/or navigational functions. In this situation,

the ICAO will support multi-State or multi-regional development of a new harmonised

navigation specification. Once the new navigation specification is complete, it will ultimately

be incorporated into the PBN Manual, Volume II.

Although the airspace concept and navigation functional requirements developed in Process

1 form the starting point of the development of a new navigation specification, it is likely that

these will need iterative refinement, in order to align them with the details of the new

navigation specification as it is being developed.

iii. Step 3: Identification and development of associated ICAO provisions.

The development of a new navigation specification may require the development of new

ICAO provisions, for example, procedure design (PANS-OPS (ICAO Doc 8168)) criteria or

ATM procedures. While these tasks are formally carried out by experts, a State(s) or region(s)

would be expected to identify changes that need to be introduced to enable the new

navigation specification and applications.

iv. Step 4: Safety assessment.

In accordance with the provisions included in the ICAO Annex 11 — Air Traffic Services and

PANS-ATM (ICAO Doc 4444), a full safety assessment of the new navigation specification

should be completed (see the Safety Management Manual (SMM) (Doc 9859). This safety

assessment is undertaken once the new navigation specification is sufficiently mature. See

PBN Manual, Volume II , Part A, Chapter 2 — Safety Assessment, for a more detailed

discussion of the necessary elements of safety assessment and risk modelling.

v. Step 5: Follow-up.

Where the above evaluation leads to the conclusion that the proposed new navigation

specification can be applied in the ATM environment, the State or region will be required to

formally notify the ICAO of the proposed application. The ICAO will take action to include the

new navigation specification into Volume II of the PBN manual.

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Upon completion of the new navigation specification development, the State or region would

then continue with Process 3: Planning and implementation.

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5 CHANGES IN ATS DELIVERY DUE TO PBN IMPLEMENTATION

Air traffic controllers and other air traffic services providers become involved with PBN at a tactical

level, as they and pilots use the PBN concept in real-time operations. They rely on the preparatory

work completed at strategic level by other stakeholders (i.e. airspace planners, procedure designers

and regulatory authorities).

This section will address only the basic changes expected in the provision of ATS, as specific

procedures will only be developed at a later stage in accordance with the PBN Implementation

Roadmap.

5.1 ATS Flight Plan Requirements

As discussed in previous sections, aircraft should be equipped with a RNAV system able to

support the desired navigation application. The RNAV system and aircraft operations must be

compliant with regulatory material that reflects the navigation specification developed for a

particular navigation application and approved by the appropriate regulatory authority for the

operation. This approval is indicated to ATS by inserting appropriate designations in Item 10

(Equipment) on the ATS Flight Plan.

Radio communication, navigation and approach aid equipment is indicated in Item 10 of the

ATS flight plan as follows:

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Insert one letter as follows:

N If no COMM/NAV/Approach aid equipment for the route flown is carried, or the equipment is unserviceable; OR

S If standard COM/NAV/Approach aid equipment for the route to be flown is carried and serviceable (standard equipment in the RSA is considered to be VHF RTF, ADF, VOR and ILS).

AND/OR

Insert one or more of the following letters to indicate the COM/NAV/Approach aid equipment

available and serviceable:

A (Not allocated)

B (Not allocated)

C LORAN C

D DME

E (Not allocated)

F ADF

G GNSS

H HF RTF

I Inertial Navigation

J Data Link (Specify in Item 18 the equipment carried, preceded by DAT/ followed by one or more letters as appropriate.)

K MLS

L ILS

M Omega

O VOR

P (Not allocated)

Q (Not allocated)

R RNP type certification (Inclusion of letter R indicates that an aircraft meets RNP type prescribed for the route segment(s), route(s) and/or area concerned.)

T TACAN

U UHF RTF

V VHF RTF

W

} When prescribed by ATS X

Y

S Other equipment carried (Specify in Item 18 the other equipment carried. Preceded by COM/ and/or NAV/ , as appropriate.)

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5.1.1 Conventional Navigation

When aircraft use conventional navigation,

aircraft normally navigate using external electronic guidance or self-contained

information;

external guidance is provided by ground-based NAVAIDs or from GNSS; and

traditional route structures are followed between the NAVAIDs.

NAVAIDs used include NDBs and VORs, and routes are defined by geographical positions of

NAVAIDs or fixes based on the intersection of radial from two NAVAIDs or a distance and a

bearing from one. Aircraft are required to overfly these NAVAIDs and fixes.

Conventional Navigation via ground-based NAVAIDs

5.1.2 Non-Conventional Navigation

Area Navigation (RNAV) is a method of navigation which permits aircraft operation on any

desired flight path within the coverage of station-referenced navigation aids or within the limits

of the capability of self-contained aids, or a combination of these.

Area Navigation – Aircraft fly desired path

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5.1.3 Designation of RNAV Routes

RNAV routes are defined by significant points called Waypoints, which are, in turn, defined by

co-ordinates. These routes can follow any desired path and are not constrained by the

position of ground-based NAVAIDs.

In the example below, the RNAV route uses DME/DME as the NAVAID to provide positional

information:

Each point on the desired route is characterised by ranges from a pair of DMEs.

The aircraft‘s computer (e.g. FMS) will estimate its position and provide guidance to the

track.

A position is estimated by the ranges from two suitably situated DMEs.

Two range rings will give two possible positions, but the navigation computer will

exclude the ―point of ambiguity‖.

Track Position 1

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Track Position 2

5.2 ATS Procedures

RNAV implementation allows ATC the possibility for the systematic use of ―DIRECT TO‖ in the overall

management of air traffic as all RNAV certified aircraft are capable to execute ―DIRECT TO‖

waypoints. Where appropriate, ATC could consider ―DIRECT TO‖ as an alternative to radar vectoring

for RNAV capable aircraft as the use of ―DIRECT TO‖ instead of radar vectoring allows RNAV

systems to maintain ―distance to go‖ information. The following advantages will be derived:

The RNAV system and pilot are aware of distance to touch down for aircraft management, and

RNAV-equipped aircraft may derive maximum benefit from RNAV systems in terms of optimised

flight management and performance.

However, be aware that pilots may not be able to comply with a ―DIRECT TO‘ for any of the following

reasons:

Navigation computer problem,

Too close to waypoint specified,

Angle of turn/speed too great,

Waypoint not displayed on the FMS for pilot selection,

Waypoint not part of SID/STAR, and/or

SID/STAR not assigned.

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If pilots are unable to comply, they will probably request radar vectors, but be aware that large turns

close to the waypoint or at high speed, may result in the aircraft overshooting the next leg.

5.2.1 Control Procedures

(FUTURE DEVELOPMENT)

a. Aerodrome (including Tower Control, Ground Control and Clearance Delivery)

b. Approach - Procedural, Radar and Automatic Dependant Surveillance (ADS)

c. Area - Procedural, Radar and ADS (including Flight Information Service & Oceanic)

d. Central Airspace Management Unit (CAMU) and the Briefing Office

5.2.2 Contingency Procedures

The pilot must notify ATC when the RNAV performance ceases to meet the requirements for

RNAV. The communication to ATC must be in accordance with the authorised procedures. In

the event of communication failure, the flight crew should continue with the flight plan in

accordance with the published ―lost communication‖ procedure.

The pilot must notify ATC of any loss of RNAV capability, together with the proposed course

of action. The loss of RNAV capability includes any failure or event causing the aircraft to no

longer satisfy the RNAV requirements of the route.

Where stand-alone GNSS equipment is used:

In the event that there is a loss of RAIM detection function, the GNSS position may

continue to be used for navigation. The flight crew should attempt to cross-check the

aircraft position, with other sources of position information, (e.g. VOR, DME and/or NDB

information) to confirm an acceptable level of navigation performance. Otherwise, the

flight crew should revert to an alternative means of navigation and advise ATC.

In the event that the navigation display is flagged invalid due to a RAIM alert, the flight

crew should revert to an alternative means of navigation and advise ATC.


a. Aerodrome (including Tower Control, Ground Control and Clearance Delivery)

b. Approach - Procedural, Radar and Automatic Dependant Surveillance (ADS)

c. Area - Procedural, Radar and ADS (including Flight Information Service & Oceanic)

d. Central Airspace Management Unit (CAMU) and the Briefing Office

e. Contingency Procedures relating to Mach Number Technique

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5.3 Separation Minima

Vertical and horizontal (lateral and longitudinal) separation minima as per ICAO Doc 4444 and SA

CAA ATS Standards and Procedures Manual (as amended) are to be applied in the provision of ATS

to aircraft utilising PBN.

5.3.1 Longitudinal


5.3.2 Lateral


5.4 Mixed Equipage Environment

A mixed navigation environment introduces some complexity for ATS. From an ATC workload and

associated automation system perspective, the system needs to include the capability of filtering

different navigation specifications from the ATC flight plan and conveying relevant information to

controllers. For ATC, particularly under procedural control, different separation minima and route

spacing are applied as a direct consequence of the navigation specification.

Mixed navigation environments usually occur in one of three scenarios:

One RNAV or one RNP application has been implemented (but not as a mandate), and

conventional navigation is retained. An example of this would be if RNAV 1 were the declared

RNAV specification for a Terminal Airspace, with the availability also of procedures based on

conventional navigation, for those aircraft not RNAV 1 approved.

A ―mixed-mandate‖ is used within an airspace volume, usually en-route or oceanic/remote

procedural operations. For example, it is mandatory to be approved to a RNAV 1 specification for

operation along one set of routes, and Basic RNP 1 along another set of routes within the same

airspace;

A mix of RNAV and RNP applications is implemented in airspace, but there is no mandate for

operators to be able to perform them. Here again, conventional navigation could be authorised for

aircraft that are not approved to any of the navigation specifications.

Mixed navigation environments can potentially have a negative impact on ATC workload, particularly

in dense en-route and terminal area operations. The acceptability of a mixed navigation environment

to ATC is also dependent on the complexity of the ATS route or SID and STAR route structure and

upon availability and functionality of ATC support tools. The increased ATC workload normally

resulting from mixed mode operations has resulted in the need to limit mixed-mode operations to a

maximum of two types where there is one main level of capability. In some cases ATC has been able

to accept a mixed environment where 90% of the traffic is approved to the required navigation

specification; whereas in other instances, a 70% rate has been workable.

For these reasons, it is crucial that operations in a mixed navigation environment be properly

assessed in order to determine the viability of such operations.

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5.5 Transition between Different Operation Environments


5.6 Phraseology

RTF phraseologies for RNAV are to be used as follows;

When checking if aircraft is able to accept a SID/STAR, ATC will use ―ADVISE IF ABLE

(designator) DEPARTURE [or ARRIVAL]‖ e.g. ―KLM123 ADVISE IF ABLE SNAKE ONE ALPHA

ARRIVAL.‖

If aircraft is unable to accept ATC issued RNAV SID/STAR, pilot will use ―UNABLE (designator)

DEPARTURE [or ARRIVAL] DUE RNAV TYPE‖ e.g. ―KLM921 UNABLE BILBO ONE ALPHA

ARRIVAL DUE RNAV TYPE, KLM921.‖ In this case ATC will seek to provide an alternative

routeing.

If aircraft is unable to continue with RNAV operations due to some failure or degradation of the

RNAV system, pilot will use ―UNABLE RNAV DUE EQUIPMENT.‖ Aircraft in flight which

announce to ATC loss of RNAV capability should be provided with radar vectors, routed via

conventional routes or routed direct to conventional NAVAIDs. For arriving aircraft in the TMA,

radar vectors could be the most efficient reversionary means.

If ATC is unable to assign a RNAV SID/STAR requested by a pilot, for reasons associated with

the type of on-board RNAV equipment indicated on the FPL, ATC shall inform the pilot using

―UNABLE TO ISSUE (designator) DEPARTURE [or ARRIVAL] DUE RNAV TYPE‖.

5.7 Reporting of Gross Navigational Errors

Gross Navigational Errors (GNEs) must be reported to the relevant regulatory authority as a condition

of approval. GNEs are defined as:

Horizontal navigation errors of 25 NM or more;

Vertical navigation errors of 300 ft or more;

Longitudinal navigation errors of three minutes or more variation between the aircraft‘s estimated

time of arrival at a reporting point and its actual time of arrival; and

Navigation system failures.

Most common causes of GNEs are failure to follow clearance, incorrect waypoint entry, climb or

descent without clearance and ATC misunderstanding. To avoid GNEs, pilots are encouraged to

following these best practises:

Good cockpit SOPs,

Verify clearances, and

Check position ten minutes after crossing waypoint.

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5.8 RNAV STARs and SIDs

RNAV systems dynamically update the ―active‖ waypoints. As waypoints are passed, they are

removed from the ―active‖ waypoints list. Therefore, be aware that aircraft can have considerable

difficulty manoeuvring ―DIRECT TO‖ a waypoint which is considered by the RNAV system, to have

been passed. ATC should make use of ―DIRECT TO‖ instructions only for waypoints on the assigned

SID/STAR, and ―DIRECT TO‖ should only be used for waypoints ahead of the aircraft.

If the pilot has been cleared for a SID/STAR and ATC consequently have to issue a ‗DIRECT TO‖ a

waypoint that is part of the SID/STAR, the following applies:

The pilot selects the waypoint in the FMS,

The FMS and navigation display are updated maintaining all details of the route from the

―DIRECT TO‖ waypoint onwards, and

The aircraft continues with the SID/STAR after reaching the waypoint.

The aircraft is expected to meet level restrictions if published, if the cleared level makes this possible.

The aircraft is also expected to meet speed restrictions if published. Be aware however, that a

―DIRECT TO‖ could shorten track miles to the waypoint, which could have an impact on the aircraft‘s

ability to meet level and speed restrictions.

If the pilot has been cleared for a SID/STAR and ATC consequently have to issue a ‗DIRECT TO‖ a

waypoint that is not part of the SID/STAR, the following applies:

Waypoints not held in the navigational database are not to be manually inserted for aircraft

operations in the TMA.

It will take time for the pilot to retrieve the waypoint from the database.

The clearance for the SID/STAR is cancelled and previously loaded SID/STAR is dropped from

the RNAV system.

No further routeing is maintained or displayed.

The aircraft requires explicit routeing after the waypoint from ATC.

If no further explicit routeing information from ATC is received, the RNAV system will revert to

―present heading mode‖ after reaching the waypoint. That means that the aircraft will continue on

from the waypoint on the heading it is on when it arrives there, unless otherwise instructed.

Be aware that the aircraft reaction could be delayed and that this process is prone to error, therefore

ATC should rather consider the use of radar vectors if routeing away from a SID/STAR is required.

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5.8.1 Related Control Procedures

The use of RNAV does not change

existing ATC and pilot

responsibilities. It does not relieve:

Pilots of their responsibility to

ensure that any clearances are

safe in respect to terrain

clearance.

ATC of its responsibility to

assign levels which are at or

above established minimum

flight altitudes.

The pilot still remains responsible for

terrain clearance. When an IFR flight

is being radar vectored by ATC or is given a direct routeing off an ATS route, the radar

controller shall issue clearances such that the prescribed obstacle clearance exists, the pilot

must also ensure flight operations conform to published minimum flight altitudes and must

inform ATC of any inability to accept a clearance or instruction on the basis of terrain

clearance issues.

5.8.2 Radar Vectoring Techniques

If minimum radar vectoring altitudes are to be used by ATC as the basis for assigning levels

in conjunction with RNAV clearances/instructions, a Radar Minimum Altitude Chart should be

published to allow pilots to comply with their responsibilities with regard to terrain avoidance.

Note: Be aware that

RNAV ―DIRECT TO‖

instructions are not radar

vectors.

If ATC issues radar

vectors whilst an aircraft is

flying a RNAV SID/STAR,

ATC should be aware that

the pilot may require

considerable manipulation

of the RNAV system in

order to resume a

SID/STAR cancelled by

ATC, (i.e. the pilot may

have difficulty in

establishing the actual

sequence of active

waypoints, as a function of

the aircraft‘s position).

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For arriving aircraft, if radar vectoring is initiated, ATC should consider continuing with radar

vectoring until the aircraft intercepts the final approach aid, e.g. ILS. If radar vectoring is

initiated for departing aircraft, ATC should consider remaining with radar vectoring until the

aircraft is in a position to join the en-route ATS route structure, or issuing a ―DIRECT TO‖ the

last waypoint of the RNAV SID.

5.8.3 Open and Closed STARs

PBN makes it possible to design closed or open STARs. Although ―open‖ or ―closed‖ STARs

are not the ICAO expressions, these terms are increasingly common in use. The choice of

open or closed procedure needs to take account of the actual operating environment and

must take into account ATC procedures.

Open STARs provide

track guidance (usually)

to a downwind track

position from which the

aircraft is tactically

guided by ATC to

intercept the final

approach track. An open

STAR will require tactical

routeing instructions to

align the aircraft with the

final approach track. This

results in the RNAV

system being able to

descend only to the final

point on the procedure

and, where path

stretching is applied by

ATC, will impact the ability of the RNAV system to ensure a continuous descent profile.

Closed STARs provide track guidance right up to the final approach track whereupon the

aircraft usually intercepts the ILS. The closed STAR provides the pilot with a defined distance

to touch down thus supporting the RNAV system‘s execution of the vertical profile. Where

multiple arrival routes are

operated onto a single

runway, the closed

procedure can result in a

safety hazard should

ATC not be able to

intervene to prevent the

automatic turn onto final

approach towards other

traffic. Significantly,

however, closed STARs

can be designed and

published in a manner

that anticipates

alternative routeing to be

given by ATC on a

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tactical basis. These tactical changes may be facilitated by the provision of additional

waypoints allowing ATC to provide path stretching or reduction by the use of instructions

―direct to a waypoint‖. However, these tactical changes, needed to maximise runway capacity,

do impact on the vertical profile planned by the RNAV system

5.8.4 Altitude Constraints


5.8.5 Descend/Climb Clearances

Three main categories of level information are used, i.e. minimum flight altitudes, cleared

levels and level restrictions.

Minimum flight altitudes (MFAs) can be considered as:

Minimum sector altitudes (MSAs)

Minimum radar vectoring altitudes (MRVAs)

Area minimum altitudes (AMAs)

Minimum flight altitudes published for segments of SIDs and STARs.

MFAs are calculated to ensure safe terrain clearances. It should be noted that currently it is

not mandatory to publish MRVAs, although it is recommended by the ICAO.

Cleared levels could be published as a written ―CLIMB TO/DESCEND TO (level)‖, ATC

expect aircraft to climb/descend to that level. These are mostly published as elements of SIDs

and have limited application for STARs. Explicitly cleared levels are issued by ATC on RTF

and override published cleared levels.

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Level restrictions are shown on charts in conjunction with waypoints where required, but do

not represent authorisation to climb/descend to that level, as it is published for purposes of

strategic airspace/traffic segregation. Pilots must comply with level restrictions to the extent

the cleared level makes it possible.

For arriving aircraft, published level restrictions, which are at or above the cleared level which

is in effect, shall be complied with. For departing aircraft, published level restrictions, which

are at or below the cleared level which is in effect, shall be complied with.

5.9 RNP Approach and Related Procedures

Waypoint speed restrictions may be published on charts in conjunction with selected waypoints where

required. ATC is free to cancel published speed restrictions at their own discretion. Explicit speed

restrictions override published ones. Be aware that adjusting speeds could have an impact on turn

performance (track) and vertical profiles.

5.10 Impact of Requesting a Change to Routing during a Procedure


5.11 Fix/Waypoint Naming

In the ICAO Annex 11 and Doc 8168, the term ―waypoint‖ is only used to define ―RNAV routes and

flight paths of aircraft employing RNAV systems‖, while the term ―significant point‖ is used, in Annex

11, to describe a ―specified geographical location used in defining an ATS route or the flight path of an

aircraft and for other navigation and ATS purposes‖. It follows from this definition that all waypoints

are significant points, even when additional waypoints are established for RNAV procedures on, or

off-set from, the arrival/approach tracks, to allow the ATS provider to de-conflict and sequence RNAV

traffic.

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In many other documents, a waypoint is also described as a fix. This is especially the case in the

terminal area where the initial approach fix (IAF), the intermediate fix (IF), the final approach fix (FAF)

and the missed approach holding fix (MAHF) are commonly used terms. In order to avoid confusion,

the ICAO has decided to continue to use the terms IAF, IF, FAF and MAPt in both conventional and

RNAV instrument approach definitions.

As a general principal, the procedure designer should ensure that all RNAV waypoints are named and

that the published names are appropriate for use in the navigation database.

Navigation databases can hold waypoint names but usually operate with waypoint (fix) identifiers

which are five characters long, known as the 5 Letter Name Code (5LNC). The ICAO requires that all

significant points are identified by 5LNCs. However, waypoints marked by the site of a NAVAID,

should have the same name and coded designator as the NAVAID. NAVAIDs are usually annotated

with the associated three-letter designator on the aircraft displays but 5LNCs should be used where

three-letter designators are not available.

While the responsibility for issuing waypoint names lies with the ICAO regional office, individual

States should exercise great care when selecting new waypoint or NAVAID names to ensure that they

are not already in use.

The following table provides guidelines for naming waypoints:

Area of Application General Usage Name Type

En-route waypoints En-route environment

5-letter globally unique

pronounceable ICAO

name code

Final waypoint SID

Terminal airspace

procedures and transition

to en-route


pronounceable ICAO

name code

Initial waypoint STAR

Terminal airspace

procedures and transition

from en-route


pronounceable ICAO

name code

Waypoints common to more than one terminal

airspace or used in a procedure common to

more than one airport in a single terminal

airspace which are not used for en-route

Terminal airspace

procedures


pronounceable ICAO

name code

Waypoints unique to an aerodrome, with a

properly assigned 4-letter location indicator,

used for terminal airspace procedures

(includes waypoints designated by the ATS

provider as requiring prominent display or as

having the function of an activation point)

Terminal airspace

procedures


pronounceable ICAO

name code, or

5-digit alphanumeric

name code specific to

the terminal airspace

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Waypoint and NAVAID co-ordinates are published in the AIP. Co-ordinates specifically associated

with an aerodrome are published in the appropriate aerodrome entry. The following chart symbols (as

detailed by ICAO Annex 4) should be used to indicate various waypoint types:

Waypoint Description Symbol

Fly-by waypoint

Fly-over waypoint

Fly-by waypoint coincident with significant point (compulsory

reporting point)

Fly-over waypoint coincident with VOR/DME

Fly-by waypoint coincident with NDB

5.12 NAVAID Infrastructure Status Monitoring

The NAVAID infrastructure to support radio navigation updating prior to entry into various RNAV/RNP

airspace (includes the status of GNSS) should be monitored and maintained and timely warnings of

outages should be issued through NOTAM.

5.13 ATS System Monitoring

Monitoring of navigation performance is required for two reasons:

Demonstrated ―typical‖ navigation accuracy provides a basis for determining whether the

performance of the ensemble of aircraft operating on the RNAV routes meets the required

performance; and

The lateral route spacing and separation minima necessary for traffic operating on a given route

are determined both by the core performance and upon normally rare system failures.

Both lateral performance and failures need to be monitored in order to establish the overall system

safety and to confirm that the ATS system meets the required target level of safety.

Radar observations of each aircraft‘s proximity to track and altitude are typically noted by ATS

facilities and aircraft track-keeping capabilities are analysed.

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A process should be established allowing pilots and controllers to report incidents where navigation

errors are observed. If an observation/analysis indicates that a loss of separation or obstacle

clearance has occurred, the reason for the apparent deviation from track or altitude should be

determined and steps taken to prevent recurrence.

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