instrument landing system

1. INSTRUMENT LANDING
SYSTEM
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2. Aim
To give a brief idea about instrument landing system
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3. Introduction
 The instrument landing system (ILS) is a collection of radio
transmitting stations used to guide aircraft to a specific airport
runway
 Especially during times of limited visibility. High-density airports
may be equipped on more than one runway.
 Chicago's O'Hare airport had an ILS installed on 12 runways in 1996.
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4. History
 Tests of the first ILS began in 1929.
 The first scheduled passenger airliner to land using ILS was in 1938.
A Pennsylvania-Central Airlines Boeing 247-D.
 In 1949, ICAO adapted an ILS standard developed by the US Army
as a standard system for all of its member countries.
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5. Types of Runway Approach
 1.Non-Instrument Runway
(NI): A runway intended for the operation of aircraft using visual
approach procedure
 2. Instrument Runway: A runway intended for the operation of
aircraft using instrument approach procedures
a) Non-Precision Runway (NP): An instrument runway served by
visual aids and a non-visual aid providing at least lateral
guidance adequate for a straight-in approach
b) Precision Runway (P): Allow operations with a decision height
and visibility ILS Category 1, or II, or III.
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6. Typically, an ILS includes
ILS consists of Ground Installations and Airborne Equipments
The localizer antenna is centered on the runway beyond the stop
end to provide lateral guidance
The glide slope, located beside the runway near the threshold to
provide vertical guidance
Marker beacons located at discrete positions along the approach
path; to alert pilots of their progress along the glide-path.
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7.  Each with a transmitter on the ground and receiver and signal processor in the
aircraft
 Increasingly, distance measuring equipment (DME) is located with the ILS, and
distance readouts in the cockpit are used instead of marker beacons.
 The localizer, glide slope, and marker beacons radiate continuous wave,
horizontally polarized, radio frequency energy
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Cont.…

8.  The frequency bands of operation Are,
1. Localizer, 40 channels from 108-112MHz
2. Glide slope, 40 channels from 329-335 MHz
3. Marker beacons, all on a single frequency of 75 MHz
 There are 2 equipments for Airborne Equipments, which are:
1. LLZ (Localizer) and Glide path antennas located on the aircraft
nose & ILS indicator inside the cockpit.
2. Maker beacon antennas and Maker beacon Indicator inside the
cockpit
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Cont.…
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9. How it Works
 Ground localizer antenna transmit VHF signal in direction opposite of
runway to horizontally guide aircraft to the runway center line.
 Ground Glide Path antenna transmit UHF signal in vertical direction to
vertically guide aircraft to the touchdown point.
 Localizer and Glide Path antenna located at aircraft nose receives both
signals and sends it to ILS indicator in the cockpit.
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Cont.…

10.  These signals activate the vertical and horizontal needles inside the
ILS indicator to tell the pilot either go left/right or go up/down.
 By keeping both needles centered, the pilot can guide his aircraft
down to end of landing runway aligned with the runway center line
and aiming the touch down.
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Cont.…
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11. LOCALIZER ANTENNA ARRAY
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12.  Localizer transmit two signals which overlap at the center.
 It operates in the VHF band: 108MHz to 117MHz.
 The left side has a 90 Hz modulation and the right has a 150 Hz modulation.
 The overlap area provides the on-track signal
Ex:- If an aircraft approaching the runway center line from the right, it will
receive more of the 150 Hz modulation than 90Hz modulation.
 Difference in Depth of Modulation will align the aircraft with the runway
center line
12 How Localizer (LLZ) works
Cont.…

13.  This deviation signal drives the left-right needle of the pilot’s cross-pointer
display (or flight director )and may be wired to the autopilot/flight-control
system for “coupled” approaches.
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Cont.…
left-right needle
cross-pointer display

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 Airplane Approaching to the
left of runway center line.
 Observe the yellow NAV
vertical pointer line tracking
the runway center line and
moving towards right.

15.  Transmit two signals which overlap at the center. The left side has a 90
Hz & right has a 150 Hz modulation. The overlap area provides the on-
track signal.
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16. GLIDE SLOPE
ANTENNA
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17. How Glide slope/path(GS/GP)indicator works
 GS operates in UHF band: 329 to 335 MHz
 Glide path antenna produces two signals in the vertical plane.
 The upper has a 90 Hz modulation and the bottom has a 150 Hz
modulation.
 For example, if an aircraft approaching the runway too high, it will
receive more of the 90 Hz modulation than 150Hz modulation.
 Difference in Depth of Modulation will align the aircraft with the glide
path.
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 Glide path produces two signals in the vertical plane.
 The upper has a 90 Hz modulation and the bottom has a 150 Hz
modulation.
(Airplane Approaching on glide path.
Observe the GS horizontal pointer line tracking on glide path and steady)

19. Marker
beacon
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20. How Marker Beacon works
 Marker beacons operating at a carrier frequency of 75 MHz.
 When the transmission from a marker beacon is received it activates
an indicator on the pilot's instrument panel.
 The correct height the aircraft should be at when the signal is received
in an aircraft.
 They aid in indicating the distance of the aircraft from the runway too.
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22. Outer Marker Beacon
 The outer marker is normally located 7.2 to 10 km from the runway threshold.
 The purpose of this beacon is to provide height, distance, and equipment
functioning checks to aircraft on intermediate and final approach.
 On the aircraft, the signal is received by a 75 MHz marker receiver. The pilot
hears a tone from the loudspeaker or headphones and a blue indicative bulb
lights up
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23. Middle Marker Beacon
 The middle marker should be located so as to indicate, in low visibility conditions
 The missed approach point, and the point that visual contact with the runway is
imminent, ideally at a distance of approximately 1,100 m from the threshold.
 The cockpit indicator is an amber lamp that flashes in unison with the received
audio code
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24. Inner Marker Beacon
 The inner marker will be located so as to indicate in low visibility conditions the
imminence of arrival at the runway threshold.
 Ideally at a distance of approximately 300 m from the threshold. The cockpit
indicator is a white lamp that flashes in unison with the received audio code
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25. Summery
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26. Thank you…….!
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