Instrument Landing System is a sort of slide passage made of radio signal depending on which aircraft can be brought safely on the runway. ILS consists of –

  1. Two glide scope pointer
  2. Two localizer pointer
  3. Outer Marker Beacon
  4. Middle Marker Beacon
  5. Inner Marker Beacon
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Instrument Landing System

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Both the pointers and the outer Marker Beacon operate at the same frequency. When the frequency of both localizer pointer pointer is tuned, the aircraft is aligned at the correct course i.e. centre of an airport runway.

Glide Scope Pointers

The two Glide Scope Pointers make the aircraft approach the correct height. One pointer indicates to fly upwards and the other pointer indicates to fly downwards to achieve correct height.

Localizer Pointers

The two Localizer Pointers help the aircraft to achieve correct position horizontally i.e. the centre of the runway. It produces radio courase aligned with the cetre of the runway.

Outer Marker Beacon

The Outer Marker Beacon indicates that the aircraft is 4.5 Nautical Miles away from the runway. As the aircraft crosses Outer Marker Beacon, purple colour light glows in the cockpit as the visual indication.

Middle Marker Beacon

The Middle Marker Beacon indicates that the aircraft is 0.25 – 0.5 Nautical Miles away from the runway. As the aircraft crosses Middle Marker Beacon, amber colour light glows in the cockpit as the visual indiacation.

Inner Marker Beacon

The Inner Marker Beacon indicates that the the aircraft is 0 Nautical Miles away from the runway. It is the start of the runway. As the aircraft crosses the Inner Marker Beacon, white coulor light glows, indicating that the aircraft is about to land.

Disadvantages of the Instrument Landing System

  • Only 40 channels are availble across the world to use the Instrument Landing System.
  • Glide scope beams & Azimuth are fixed and narrow. As a result of this, the aircraft course has to be squeezed & adequately seperated which causes landing delays.
  • No special procedures are available for slower aircraft, helicopters & for short take-off and landing aircraft.
  • ILS can’t be sited in hilly terrain & requires large expenses of flat clear land to minimize interference between localizer and glide scope beams.
  • Vehicle taxing & low flying of aircraft & welding have to be kept away from the transmission site to avoid localizer and glide scope course deviation.

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