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Lecture 6: I NSTRUMENT L ANDING S YSTEM (ILS). History of ILS. 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. . Poor Visibility Landings. Poor Visibility Landings. What Is ILS?.

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  2. History of ILS 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. Poor Visibility Landings

  4. Poor Visibility Landings

  5. 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.

  6. 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.

  7. Runway Approach Precision Runway (P) Non-Instrument Runway (NI) Aiming point Touchdown zone Threshold Non-Precision Runway (NP)

  8. 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

  9. ILS Components ILS components consists of Ground Installations and Aircraft Equipments There are 2 equipments for Ground Installations, which are: Ground Localizer (LLZ) Antenna– To provide horizontal navigation Ground Glide path (GP) Antenna– To provide vertical navigation There are 2 equipments at aircrafts, which are: LLZ and GP antennas located on the aircraft nose. ILS indicator inside the cockpit

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

  11. Ils indicator in the Cockpit

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

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

  14. 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).

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

  16. 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).


  18. 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

  19. 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.

  20. ILS principles

  21. 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.

  22. VOR

  23. 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.

  24. 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.

  25. ILS Categories

  26. 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).

  27. ILS Categories • The categories are: • CAT I: DH>200 ft, RVR>2400 ft • CAT II: 100 ft< DH <200 ft, RVR>1200 ft • CAT III: in general DH<100 ft and RVR<700 ft

  28. 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

  29. Marker Beacons

  30. 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.

  31. Marker Beacons Lights in cockpit

  32. Marker Beacons

  33. 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.

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


  36. 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.

  37. 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

  38. 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.

  39. MLS Ground Installations An MLS azimuth (horizontal) guidance station

  40. MLS Ground Installations An MLS elevation (vertical) guidance station

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