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Lecture 8: I NSTRUMENT L ANDING S YSTEM (ILS). By: Zuliana Ismail,2010. History of ILS. ILS is stand for Instrument Landing System. Scheduled service would be impossible without a way to land in poor weather. The first scheduled passenger airliner to land using ILS was in 1938. .

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  1. Lecture 8:INSTRUMENTLANDING SYSTEM (ILS) By: Zuliana Ismail,2010

  2. History of ILS • ILS is stand for Instrument Landing System. Scheduled service would be impossible without a way to land in poor weather. The first scheduled passenger airliner to land using ILS was in 1938.

  3. History of ILS • 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 from Washington to Pittsburgh. • In 1949, ICAO adapted an ILS standard developed by the US Army as a standard system for all of its member countries. • 1958-First IFR landing system developed • 1966-First ILS system developed and tested at AIRPORT in USA • 1968-First ILS applications installed at major airports • 1974-ILS systems mandated by FAA for at least two major runways at all Regional, and International Airports.

  4. Poor Visibility Landings

  5. 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.

  6. Precision Runway (P) Aiming point Touchdown zone Designators Threshold

  7. 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. Precision Runway (P) Categories

  8. ILS Components ILS components consists of Ground Installations and Aircraft Equipments Ground: Ground Localizer (LLZ) Antenna– To provide horizontal navigation Ground Glide path (GP) Antenna– To provide vertical navigation Aircraft Equipments LLZ and GP antennas located on the aircraft nose. ILS indicator inside the cockpit

  9. ILS Components ILS Indicator inside the cockpit Ground Localizer Antenna Ground Glide Path Antenna

  10. Ils indicator in the Cockpit

  11. ILS Indicator Localizer indicator Deviation from runway centre line Glide path indicator Deviation from optimal glide path

  12. Localizer Indication Needle indicates direction of runway. Centered Needle = Correct Alignment

  13. 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).

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

  15. Glide 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).


  17. 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. Localizer

  18. 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.

  19. ILS principles

  20. How ILS works? • Ground localizer antenna transmit VHFsignal in direction opposite of runway to horizontally guide aircraft to the runway centre line. • Ground Glide Path antenna transmit UHF signalin 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.

  21. VOR

  22. Factors affected ILS signals Although 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.

  23. 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.

  24. Marker Beacons

  25. Marker Beacons • Marking beacon is function as ILS markers. It consists Outer , Middle and Inner Markers. • It functions to enable the pilot cross check the aircraft’s position. • When the aircraft is passing over the marker beacons, they are indicated by light illumination and Morse Code tone through the cockpit speaker or headphones.

  26. Marker Beacons

  27. Marker Beacons Lights in cockpit

  28. 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.

  29. Summary Marker Beacons: the height aircraft Localizer: horizontal guidance Glide Path: vertical guidance


  31. What is MLS? • MLS (Microwave Landing System) is an advanced landing system. MLS operates in the Super High Frequency (SHF) between 5.031 to 5.090GHz. • MLS was developed in 1978 to improve the uses of ILS system. It was chosen to replace ILS and installation date fixed to be 1995. • However , advances in GPS system led to the expectations in many countries that the life of ILS could be extended until GPS would provide accurate landing guidance. • Thus, only few countries installed MLS.

  32. Why MLS need to replace ILS? • ILS has a narrow and single approach path • ILS has 40 channels and it signals are very sensitive, example if a vehicle passes near localizer, the ILS needle in the a/c may deflect. • ILS signals are limited, as example: ILS is inflexible for helicopter landing as it has a single GP angle at any given installation.

  33. Advantages of MLS • MLS provide large coverage thus enable multiple approach paths to the same runway-horizontally & vertically. • Large number of channels (200): can minimize the risk of signal interferences. • Increase runway utilization even during poor visibility. Example: using ILS only 24 aircraft could land per hour, but with MLS, it allows an extra 6 aircraft an hour to land.

  34. MLS Ground Installations An MLS horizontal guidance station

  35. MLS Ground Installations An MLS vertical guidance station

  36. Korean Airlines Boeing 747: CFIT while attempting to land in heavy rain: 228 of 254 killed (Aug. 6, 1997)

  37. Missed Approach • On 6 August 1997, the crew of Korean Air Flight 801 initiated a missed approach while on a final approach because they were unable to see the runway, but the aircraft crashed, killing 228 people.

  38. Missed Approach • There was heavy rain at Guam so visibility was significantly reduced and the crew was attempting an instrument landing. • Air traffic control in Guam advised the crew that the Glide Path Instrument Landing System (ILS) in runway 6L was out of service. • Air traffic control cleared Flight 801 to land on runway 6L at around 1:40 am.

  39. Missed Approach • The crew noticed that the plane was descending very steeply, and noted several times that the airport "is not in sight". • At 1:42 am, the aircraft crashed into Nimitz Hill, about 3 nautical miles (5 km) short of the runway, at an altitude of 660 feet (201 m).

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