Atm Lecture 6-7

8/2/2019 Atm Lecture 6-7

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Calculation of radius of turnThe method used to calculate turn radii are applicable to aircraftperforming a constant radius turn. The material has been derived from

the turn performance criteria developed for RNP 1 ATS routes and canbe used in the construction of the required additional protected airspaceon the inside of turns also for ATS routes other than those defined byVOR.

Turn performance is dependent on two parameters ground speed andbank angle. Due to the effect of the wind component changing with the

change of heading, the ground speed and hence bank angle will changeduring a constant radius turn.

However, for turns not greater than approximately 90 degrees and for thespeed values considered below, the following formula can be used tocalculate the achievable constant radius of turn, where the ground speedis the sum of the true airspeed and the wind speed:

Radius of turn = (Ground Speed)2 -------------------------------------

Constant G * TAN(bank angle)


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The greater the ground speed, the greater will be the required bank angle.

To ensure that the turn radius is representative for all foreseeableconditions, it is necessary to consider extreme parameters.

A true airspeed of 1 020 km/h (550 kt) is considered probably the greatest

to be encountered in the upper levels. Combined with maximum anticipatedwind speeds in the medium and upper flight levels of 370 km/h (200 kt) [99.5per cent values based on meteorological data], a maximum ground speed of1 400 km/h (750 kt) should be considered.

Maximum bank angle is very much a function of individual aircraft. Aircraftwith high wing loadings flying at or near their maximum flight level are highlyintolerant of extreme angles

Most transport aircraft are certified to fly no slower than 1.3 times their stallspeed for any given configuration. Because the stall speed rises withTAN(bank angle), many operators try not to cruise below 1.4 times the stallspeed to protect against gusts or turbulence. For the same reason, manytransport aircraft fly at reduced maximum angles of bank in cruiseconditions.

Hence, it can be assumed that the highest bank angle which can betolerated by all aircraft types is in the order of 20 degrees.


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By calculation, the radius of turn of an aircraft flying at 1 400km/h (750 kt) ground speed, with a bank angle of 20 degrees, is22.51 NM (41.69 km). For purposes of expediency, this hasbeen reduced to 22.5 NM (41.6 km). Following the same logic

for the lower airspace, it is considered that up to FL 200 (6 100m) the maximum figures to be encountered are a true airspeedof 740 km/h (400 kt), with a tailwind of 370 km/h (200 kt).Keeping the maximum bank angle of 20 degrees, and followingthe same formula, the turn would be defined along a radius of

14.45 NM (26.76 km). For expediency, this figure may berounded up to 15 NM (27.8 km).

Given the above, the most logical break point between the twoground speed conditions is between FL 190 (5 800 m) and FL200 (6 100 m). In order to encompass the range of turn

anticipation algorithms used in current flight managementsystems (FMS) under all foreseeable conditions, the turn radiusat FL 200 and above should be defined as 22.5 NM (41.6 km)and at FL 190 and below as 15 NM (27.8 km).


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REQUIRED NAVIGATIONPERFORMANCE (RNP)

The Special Committee on Future Air Navigation Systems (FANS) identified

that the method most commonly used over the years to indicate requirednavigation capability was to prescribe mandatory carriage of certainequipment.

The committee developed the concept of required navigation performancecapability (RNPC).

FANS defined RNPC as a parameter describing lateral deviations fromassigned or selected track as well as along track position fixing accuracy onthe basis of an appropriate containment level

The RNPC concept was approved by the ICAO Council and was assigned tothe Review of the General Concept of Separation Panel (RGCSP) for furtherelaboration.

The RGCSP, in 1990, noting that capability and performance weredistinctively different and that airspace planning is dependent on measuredperformance rather than designed-in capability, changed RNPC to requirednavigation performance (RNP).


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The RGCSP then developed the concept of RNP

further by expanding it to be a statement of thenavigation performance necessary for operation within

a defined airspace. System use accuracy is based on the combination of

the navigation sensor error, airborne receiver error,display error and flight technical error. This

combination is also known as navigation performanceaccuracy The RNP types specify the navigation performance

accuracy of all the user and navigation systemcombinations within an airspace.

RNP types can be used by airspace planners todetermine airspace utilization potential and as an inputin defining route widths and traffic separationrequirements, although RNP by itself is not sufficient

basis for setting a separation standard.


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RNP as a concept applies to navigationperformance within an airspace and thereforeaffects both the airspace and the aircraft. RNPis intended to characterize an airspace througha statement of the navigation performance

accuracy (RNP type) to be achieved within theairspace.

The RNP type is based on a navigation

performance accuracy value that is expected to be achieved at least 95 per cent of the time by

the population of aircraft operating within the

airspace.


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The application of RNAV techniques in various partsof the world has already been shown to provide anumber of advantages over more conventional formsof navigation and to provide a number of benefits,

including: a) establishment of more direct routes permitting a reduction in flight distances; b) establishment of dual or parallel routes to

accommodate a greater flow of en-route traffic; c) establishment of bypass routes for aircraft over

flying high-density terminal areas; d) establishment of alternatives or contingency routes

on either a planned or an ad hoc basis; e) establishment of optimum locations for holdingpatterns; and

f) reduction in the number of ground navigation

facilities.


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Defining RNP airspace

RNP may be specified for a route, a number of

routes, an area, volume of airspace or any airspace of defined dimensions that an airspace planner or

authority chooses. Potential applications of RNPinclude:*

a) a defined airspace, such as North Atlantic minimum navigation performance specifications (MNPS)airspace;

b) a fixed ATS route, such as between Sydney,

Australia and Auckland, New Zealand; c) random track operations, such as betweenHawaiiand Japan; and

d) a volume of airspace, such as a block altitude on a

specified route.


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North Atlantic regional planning body established under theauspices of the International Civil Aviation Organisation (ICAO).This Group is responsible for developing the required

operational procedures; specifying the necessary services andfacilities and; defining the aircraft and operator approvalstandards employed in the NAT Region.

NORTH ATLANTIC MINIMUM NAVIGATION PERFORMANCESPECIFICATIONS AIRSPACE

The vertical dimension of MNPS Airspace is between FL285and FL420 (i.e. in terms of normally used cruising levels, fromFL290 to FL410 inclusive).

The lateral dimensions include the following Control Areas

(CTAs): REYKJAVIK, SHANWICK, GANDER and SANTA MARIA

OCEANIC plus the portion of NEW YORK OCEANIC which isNorth of 27N but excluding the area which is west of 60W &south of 3830'N

I th MNPS Ai i ft t b i d


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In the MNPS Airspace an aircraft must be equippedwith the following:

a) two fully serviceable Long Range NavigationSystems (LRNSs). A LRNS may be one of following

one Inertial Navigation System (INS); one Global Navigation Satellite System (GNSS); or one navigation system using the inputs from one or

more Inertial Reference System (IRS) or any other

sensor system complying with the MNPS requirement. Note 1: Currently the only GNSS system fully

operational and for which approval material isavailable, is GPS.

b) each LRNS must be capable of providing to theflight crew a continuous indication of the aircraftposition relative to desired track.

c) it is highly desirable that the navigation system

employed for the provision of steering guidance iscapable of being coupled to the autopilot.


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PERFORMANCE MONITORING

The horizontal (i.e. latitudinal and longitudinal)and vertical navigation performance ofoperators within NAT MNPS Airspace ismonitored on a continual basis. If a deviation isidentified, follow-up action after flight is taken,both with the operator and the State of Registryof the aircraft involved, to establish the cause of

the deviation and to confirm the approval of theflight to operate in NAT MNPS and/or RVSMAirspace.


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The Organised Track System (OTS

As a result of passenger demand, time zonedifferences and airport noise restrictions, much of theNorth Atlantic (NAT) air traffic contributes to two majoralternating flows: a westbound flow departing Europein the morning, and an eastbound flow departing NorthAmerica in the evening.

The effect of these flows is to concentrate most of the

traffic unidirectionally, with peak westbound trafficcrossing the 30W longitude between 1130 UTC and1900 UTC and peak eastbound traffic crossing the30W longitude between 0100 UTC and 0800 UTC.


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Due to the energetic nature of the NAT weather patterns,

including the presence of jet streams, consecutive eastboundand westbound minimum time tracks are seldom identical. The

creation of a different organised track system is thereforenecessary for each of the major flows. Separate organisedtrack structures are published each day for eastbound andwestbound flows. These track structures are refered to as theOrganised Track System or OTS.

It should be appreciated, however, that use of OTS tracks is notmandatory. Currently about half of NAT flights utilise the OTS.Aircraft may fly on random routes which remain clear of theOTS or may fly on any route that joins or leaves an outer trackof the OTS. There is also nothing to prevent an operator fromplanning a route which crosses the OTS. However, in this case,operators must be aware that whilst ATC will make every effortto clear random traffic across the OTS at published levels, re-routes or significant changes in flight level from those plannedare very likely to be necessary during most of the OTS trafficperiods


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Applying RNP in an airspace

Ideally, airspace should have a single RNP type;

however, RNP types may be mixed within a given airspace.

An example would be a more stringent RNP type (DMEDME)

being applied to a specific route in a very high frequency (VHF)omni directional radio range (VOR)/DME airspace or a lessstringent RNP type applied to a specific airspace.

RNP can apply from take-off to landing with the different

phases of flight requiring different RNP types. As an example,an RNP type for take-off and landing may be very stringentwhereas the RNP type for en-route may be less demanding


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Relation of RNP to separation minima

RNP is a navigation requirement and is only one factor to beused in the determination of required separation minima. RNPalone cannot and should not imply or express any separation

standard or minima. Before any State makes a decision toestablish route spacing and aircraft separation minima, theState must also consider the airspace infrastructure whichincludes

Surveillance

and communications.

In addition, the State must take into account other

parameters such as intervention capability, capacity,

airspace structure and occupancy or passing frequency


17/19

RNP is a fundamental parameter in thedetermination of safe separation standards.

The risk of collision is a function of navigationperformance, aircraft exposure, and theairspace systems ability to intervene to prevent

a collision or maintain an acceptable level ofnavigation performance. An increase in traffic ina particular airspace can result in airspaceplanners considering a change in airspace

utilization (e.g. separation minima,routeconfiguration) while maintaining an acceptablelevel of risk. In collision risk analysis, thisacceptable level of risk is referred to as thetarget level of safety (TLS)


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NAVIGATIONEXPOSURE

Route Configuration

Intervention

Traffic Density

Airspace characteristics that affect separationstandards

SurveillanceCommunication

ATC

Risk Collision=F(navigation+route Configuration+survelliance+communication+ATC)

AIRCRAFT PERFORMANCE


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AIRCRAFT PERFORMANCE

The concept of RNP is based on the expectednavigation performance accuracy of the population of

aircraft using the airspace. This in turn placesdemands on individual aircraft, manufacturers ofaircraft and aircraft operators to achieve the navigationperformance required for a specific RNP type airspaceon each flight.

The RNP concept may also require different aircraftfunctional capabilities in different types of RNP

airspaces. As an example, an RNP airspace with ahigh accuracy requirement may have functionalrequirements for parallel offset capability, whereas aless accurate RNP airspace may only require point-to-

point navigation capability

Atm Lecture 6-7

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