Instrument Landing System (ILS) · Instrument Landing System (ILS) Once established on an approach,...
Transcript of Instrument Landing System (ILS) · Instrument Landing System (ILS) Once established on an approach,...
AIR NAVIGATION PROF. A.M.ALLAM
Instrument Landing System (ILS)
Once established on an approach, pilot will follow the ILS and descend along
the glideslope, until the Decision Height (DH) is reached
At this point, the pilot must have the runway or its approach lights in sight to
continue the approach
Otherwise, the approach must be aborted and a missed approach procedure will be
performed i.e., the A/C will climb back to a predetermined altitude and position
AIR NAVIGATION PROF. A.M.ALLAM
Provides an A/C with: a precision final approach to the runway with horizontal and
vertical guidance to the runway to enable a safe landing
It uses a combination of: radio signals and, in many cases, high intensity lighting arrays
to enable a safe landing
Used by pilots landing at an airport when there is poor weather and/or low visibility
The ground equipment contains:
-Localizer transmitter (provides horizontal or lateral navigation)
-Glide path transmitter (provides vertical navigation)
-Marker beacons and/or distance measuring equipment DME (Provides distance
from runway)
-Approach lighting system (transition from instrument monitoring to visual marking
lights)
Onboard A/C equipment:
- RXs
-Localizer and glide slope antennas in the A/C nose
-ILS indicator inside the cockpit
Introduction
AIR NAVIGATION PROF. A.M.ALLAM
International Civil Aviation Organization (ICAO)
makes ILS category according to
ILS Categories
Category Decision Height (above threshold)
Runway Visual Range RVR limit Visibility
I 200 ft 550 m or 2400 ft (1800 ft is approved at some airports) 800 m
II 100 ft 350 m or 1200 ft N/A
IIIa 50 ft < DH < 100 ft 200 m (700ft) N/A
IIIb 0 < DH < 50 ft 200m > RVR limit > 75 m (150 ft) N/A
IIIc No DH No RVR N/A
Category IIIc is not yet in operation anywhere
Category IIIb is currently the best available system
AIR NAVIGATION PROF. A.M.ALLAM
ILS constellation
Approach light system
ILS indicator inside the cockpit
AIR NAVIGATION PROF. A.M.ALLAM
http://www.youtube.com/watch?v=KVtEfDcNMO8
Glide
slope
Localizer
AIR NAVIGATION PROF. A.M.ALLAM
Localizer
A localizer is a highly directive VHF ground radio transmitter in the range (108.1 – 111.95 MHz)
using the same general range as VOR transmitters to provides lateral guidance. The frequencies
of the localizer are only placed on odd decimals; where the tenths of a megacycle is odd so, for
example 108.10 and 108.15 MHz are localizer and are not used for any other purpose while 108.20
and 108.25 MHz are not, but can be allocated to VOR
It is usually located on the centerline at the opposite end of the runway
The transmitted signal is produced using a circularly polarized antenna array
The right lobe carrier is AM by 90 Hz and the other by 150 Hz tones
The localizer is identified by an audio signal superimposed on the navigational signal
To avoid interference from another localizers, every localizer has a two letter identification
preceded by the letter "I“
AIR NAVIGATION PROF. A.M.ALLAM
The array is composed of 14 separate but colocated elements. Each lobe is
produced by 7 array elements, one slightly to the left of the runway
centerline and the other to the right
The beamwidth is varied
from approximately 3º to
6º, with 5º being normal
AIR NAVIGATION PROF. A.M.ALLAM
The directivity of the localizer antenna depends on wither ,it is Back or Forward course
-A backcourse localizer is also used on some ILS systems
-A Localizer Back Course is just like a regular localizer approach except that left is right, and
right is left. In addition, it may, or may not, have a Glide Slope. If it has a Glide Slope, it is called
a "Localizer Back Course with Glide Slope"
-The backcourse is intended for landing purposes and it’s secured with a 75 MHz marker beacon
AIR NAVIGATION PROF. A.M.ALLAM
The received signal in the A/C receiver activates a vertical needle
called the Track Bar (TB) in Course Deviation Indicator (CDI)
The receiver is combined with the VOR receiver unit
The TB is deflected to the left if the A/C is east (right) of the
extended centerline of the runway (in the area modulated at 150Hz)
The TB is deflected to the right if the A/C is west (left)
of the extended centerline of the runway (in the area
modulated at 90Hz)
The A/C is
1° left of
course (shift
right to
return)
The A/C is
1° right of
course (shift
left to
return)
Represents the
difference between the
localizer position and
the A/C position
At the point where the 90 Hz and 150 Hz signals are of equal
intensity, the TB is centered, indicating that the A/C is
located precisely on the approach track (in the course)
Course Deviation Indicator
AIR NAVIGATION PROF. A.M.ALLAM
If an A/C is to the left side of the
centerline , the 90 Hz
modulation exceeds that of the
150 Hz
CDI vertical needle is deflected
towards the right side
The action is the A/C should shift right to be in the course
Operation
AIR NAVIGATION PROF. A.M.ALLAM
On the contrary, if an A/C is to
the right side of the centerline,
the 150 Hz modulation will
exceed that of 90 Hz
CDI vertical needle is deflected
towards the left side
The action is the A/C should turn left to be in the course
AIR NAVIGATION PROF. A.M.ALLAM
If the A/C on approach with the runway
centerline
CDI will display Difference in Depth of
Modulation; DDM=0 between 90 and 150
Hz and the CDI needle is centered
Implying that the plane is located exactly
in the approach axis as shown in the
figure
Localizer information is typically displayed on a CDI which is used by the pilot
until visual contact is made and the landing completed
AIR NAVIGATION PROF. A.M.ALLAM
• VHF Signal Processor: Maintains a favourable SNR ratio suitable for detection
• Signal Amplifiers: Electronic device that can increase the power of a signal
Transmitter
AIR NAVIGATION PROF. A.M.ALLAM
The onboard equipment localizer is an antenna system composed of a VHF receiver, and
is located inside the A/C
The localizer receiver and the VOR receiver form a single unit
This equipment enables to receive the localizer signal by an onboard VHF localizer
receiver, process it and to display the A/C’s position on an onboard indicator
• The indicator full scaled deflection is achieved when the DDM is 0.155
• The pilot should keep the DDM zero, where, the A/C will approach the
runway threshold along the course line
Receiver
AIR NAVIGATION PROF. A.M.ALLAM
Localizer reflected signals affect
the ILS performance and hence the
degrade quality due to scattered
beams
Localizer is sensitive to
obstructions like buildings and
terrains
Since antennas point in a single
direction, only “straight”
approaches are available
Can be costly
Microwave Landing System
-Curved approaches are possible
-Less interference and more
accurate than traditional ILS
Transponder Landing System
-Easy to deploy in remote areas
-No additional equipment needed
on A/C
Localizer limitations Localizer Enhancement
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 16
5-Glideslope
Operates at a range of 329.3-335 MHz, with a 50 KHz spacing between each channel
Provides vertical guidance (guides the pilot’s rate of
descent) of the A/C during the ILS approach
The signals are arranged unlike the localizer, on top of each
other such that the upper signal has a 90 Hz modulation and
the bottom signal has a 150 Hz modulation
A system of vertical guidance to touchdown zone in elevation
plane is provided by two overlapping lobes producing on inclined
plane of equal signal
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 17
Composed of a ground based UHF radio transmitter and antenna system,
UHF receiver in A/C receives the glide slope signal
Glide Slope (GS) or Glide Path (GP) antenna array is
located at one side of the runway touchdown zone
Is located 225–380 meters from the approach end and 120–210
meters to the side of the runway centerline
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 18
The glide path angle is normally adjusted to
3 degrees above horizontal
The thickness of the overlap area is 1.4º or 0.7º above and
0.7º below the optimum glide slope
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 19
Glide path angle is the angle between the glide path & the horizontal plane
(θo =3 degrees)
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 20
• The pilot controls the A/C so that the glide slope CDI needle remains centered on the
display to ensure the A/C is following the glide path to remain above obstructions and
reach the runway at the proper touchdown point
• Localizer (LOC) and glide slope (G/S) carrier frequencies are paired so that the
navigation radio automatically tunes the GS frequency which corresponds to the
selected LOC frequency
• The LOC signal is in the 110 MHz range (VHF) while the G/S signal is in the
330 MHz (UHF) range
• The correct frequency of the glide slope beacon is tuned automatically at the instant
when the localizer’s frequency is selected
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 21
It informs the pilot how much above or below the path, the A/C is
The pilot’s objective is to fly the A/C so that the CDI needle is
always centered
The transmitted signal contains 90 Hz & 150 Hz sidebands that are amplitude
modulated and broadcast with the RF carrier
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The glide slope receiver detects the modulations
Measures the signal strength of the tones (90,150)
Compares them against the strength of the carrier
These two quantities are the Difference in Depth of Modulation (DDM)
The DDM is then displayed for the pilot on Course Deviation Indicator (CDI)
90150 mmDDM
Operation
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 22
Indicates 150 Hz dominance ( fly UP)
Indicates 90 Hz dominance ( fly DOWN)
+ve DDM
-ve DDM
DDM=0 A/C is on the correct glide path
Indicates that 90 Hz is dominant
(fly down)
Indicates that 150 Hz is dominant
(fly up)
AIR NAVIGATION PROF. A.M.ALLAM
3/29/2020 LECTURES 23
2600 ft
4-7 miles
Runway
3500 ft
200 ft
O M M M
-Modulated audio signal at
400 Hz on a 75MHz carrier
frequency
-Blue light flashes
-Modulated audio
signal at 1300 Hz
on a 75MHz carrier
frequency
-Yellowlight flashes
I MPlaced 1000 ft before the runway
Modulated audio signal at 3000 Hz.
A White light flashes
A/C is less than 200 ft above ground
6-Maker beacons
Provide information on distance from
runway