Lecture 6:INSTRUMENT

LANDING SYSTEM (ILS)

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History of ILS

The first scheduled passenger airliner to land using ILS was in 1938.

Scheduled service would be impossible without a way to land in poor weather.

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Poor Visibility Landings

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Poor Visibility Landings

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What Is ILS?

• ILS is stand for Instrument Landing System.• ILS is a radio aid to the final approach and is

used only within a short distance to the airport.

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The Uses of ILS• To provide an aircraft with a precision final approach.

Provide both horizontal and vertical guidance.

• To guide the pilot to perform landing.– It is very helpful when visibility is limited and the

pilot cannot see the airport and runway.• To help the aircraft to a runway touchdown point.• To ensure flight safety.

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Runway Approach

7

Non-Instrument Runway (NI)

Non-Precision Runway (NP)

Precision Runway (P)

Threshold

Touchdown zone

Aiming point

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Precision Runway (P) Categories• Runway Threshold: Beginning of runway for landing.

• Touchdown zone: The first point for the aircraft should touch the runway during landing.

• Aiming point: serves as a visual aiming point for a landing aircraft.

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ILS Components• ILS components consists of Ground Installations and Aircraft

Equipments• There are 2 equipments for Ground Installations, which are:

1. Ground Localizer (LLZ) Antenna – To provide horizontal navigation

2. Ground Glide path (GP) Antenna – To provide vertical navigation

• There are 2 equipments at aircrafts, which are:

1. LLZ and GP antennas located on the aircraft nose.

2. ILS indicator inside the cockpit

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ILS ComponentsILS Components

Ground Localizer Antenna Ground Glide Path

Antenna

ILS Indicator inside the cockpit

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ILS INDICATOR IN THE COCKPIT

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ILS Indicator

Glide path indicator

Deviation from optimal glide path

Localizer indicatorDeviation from runway

centre line

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Localizer Indication

Needle indicates direction of runway.Centered Needle = Correct Alignment

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Localizer Indication

• The vertical needle is the localizer indicator.• It provides the pilot with information required

for horizontal.• The localizer needle is tracked horizontally by

adjusting the position aircraft in the direction of the needle (fly right or fly left).

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Glide Path IndicationsGlide Path Indications

Needle indicates above/below glide path.Centered Needle = Correct Glide path

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Glide Path IndicationsGlide Path Indications

• The horizontal needle is the glide path indicator.

• It provides the pilot with information required for vertical guidance.

• The glide path needle is tracked vertically by adjusting the rate of descent in the direction of the needle (fly up or fly down).

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ILS GROUND INSTALLATIONS

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Localizer• Localizer is the horizontal antenna array located at the opposite end of the runway.• Localizer operates in VHF band between 108 to 111.975 MHz.• Normal reliable coverage of localizers is between 10 nm to 25nm.

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Glide Path• Glide Path is the vertical

antenna located on one side of the runway about 300 m to the end of runway.

• Glide Path operates in UHF band between 329.15 and 335 MHz

• The GP signals coverage extends to a distance of 10nm.

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ILS PRINCIPLES

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How ILS works?• Ground localizer antenna transmit VHF signal in direction

opposite of runway to horizontally guide aircraft to the runway centre 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.

• 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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VOR

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Factors affected ILS signalsAlthough the ILS system is very accurate and precise, it is very

sensitive and its operation can be adversely affected by weather, FM broadcasts and vehicle/aircraft movement on the ground.

• Weather

Snow and heavy rain attenuates the ILS signals thereby reducing the accuracy.

• FM broadcasts

FM transmitters (radio stations) have wide bandwidths and it is possible for such stations transmitting on same frequencies that causing interference with the ILS signals.

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Factors affected ILS signals

• Vehicle or aircraft movement on the ground. – Every ILS installation has its critical area and its

sensitive area. – The critical area is protected during all ILS

operations because the presence of vehicles or aircraft inside its boundaries will cause unacceptable disturbance to the ILS signals.

– Thus, these areas are important to prevent ILS signal disturbance.

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ILS CATEGORIES

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ILS Categories

• ILS categories depends on 2 things, which are Decision Height (DH) & Runway Visual Range (RVR).

• The Decision Height (DH) is the altitude when the pilot must see the runway lights, else he must abort the landing.

• Runway Visual Range (RVR) means how far pilot can see on horizontal plane (how many feet pilot can see).

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ILS Categories

• The categories are:

1. CAT I: DH>200 ft, RVR>2400 ft

2. CAT II: 100 ft< DH <200 ft, RVR>1200 ft

3. CAT III: in general DH<100 ft and RVR<700 ft

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Example ILS CAT II/III• The following must be fully serviceable to meet CAT II/III standards:• Airport lighting:

– Approach lights– Runway threshold lights– Touchdown zone lights– Centerline lights– Runway edge lights– Runway end lights– All stop bars and lead-on lights– Essential taxiway lights

• ILS components:– Localizer– Glide path

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MARKER BEACONS

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Marker Beacons

• A marker beacon is a particular type of VHF radio beacon used in aviation, usually in conjunction with an Instrument Landing System (ILS).

• When the aircraft is passing over the marker beacons, they are indicated by illumination of the corresponding light in the cockpit and by emitting of the coded tone (Morse code) through the cockpit speaker or headphones.

• The function of marker beacon is to enable the pilot cross check the aircraft’s position.

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Marker Beacons Lights in cockpit

Marker beacon Cockpit light Identification Volume pitch

Outer marker Blue 2 dashes / second Low

Middle marker Amber Alternate dots and dashes 3 / second Medium

Inner marker White 6 dots / second High

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Marker Beacons

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Marker Beacons

Outer marker• The outer marker should be located about 7km from the

threshold.• The cockpit indicator is a blue lamp that flashes accordingly

with the received audio code. Middle marker• Ideally at a distance of 1km from the threshold. • The cockpit indicator is an amber lamp that flashes in

accordingly with the received audio code. Inner marker• Located at the beginning (threshold) of the runway .• The cockpit indicator is a white lamp that flashes in

accordingly with the received audio code.

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Summary

34

Localizer: horizontal guidanceGlide Path:

vertical guidance

Marker Beacons: the height aircraft

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MICROWAVE LANDING SYSTEM

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What is MLS?

• MLS (Microwave Landing System) is an advanced precision approach and landing system.

• MLS was developed to improve the uses of ILS system, however only few Airports have MLS installations.

• MLS operates in the Super High Frequency (SHF) between 5.031 to 5.090GHz.

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Advantages of MLS• MLS provide large coverage signals even in very poor

visibility.• As MLS signals have large coverage, this will increase

runway utilization.• MLS also has more channels which can avoid the signal

interferences.

MLS Coverage

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MLS vs ILS• Aircraft flying into Heathrow Airport in fog or poor visibility.• On a clear day, about 44 planes an hour land at Heathrow. • However, if the visibility drops and aircraft have to use the

ILS system to land, only 24 aircraft could land per hour. • This is because the radio transmitter at the end of the

runway needs good line of sight to the approaching aircraft, but because it is at the far end of the runway, planes have to land and taxi clear before a full signal is restored.

• However, MLS allows an extra six aircraft an hour to land, meaning that while fog will still cause disruption, its effects will be less prominent.

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MLS Ground Installations

An MLS azimuth (horizontal) guidance station

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MLS Ground Installations

An MLS elevation (vertical) guidance station