An Aircraft uses Navigation aid likes Automatic Direction Finder (AD F), VHF omnidirectional range (VOR), Distance Measurement Instrument (DME) for Guidance and to navigate but these Aids can't used to land an aircraft. Hence system designed for landing of aircraft is Instrument Landing System (ILS).
The instrument Landing System is an internationally normalized for navigation of aircraft upon the final approach for landing. It was accepted as a standard system by the ICAO (International Civil Aviation Organization) in 1947.
ILS uses a combination of VHF and UHF radio waves.It consists of four subsystems:
LOCALIZER: One of the main component of the ILS System is the Localizer which handle the guidance in the horizontal plan. Localizer is an antenna system comprised of a VHF transmitter which uses the same frequency range as a VOR transmitter (108-112 MHz) in 0.5MHz increments.
Localizer emits two directional radiation patterns. One comprises of a bearing amplitude-modulated wave with a harmonic signal frequency of 150Hz an the other one with the same bearing amplitude-modulated wave with a harmonic signal frequency of 90Hz. These two directional radiation patterns do intersects and thus create a course plane, or a horizontal axis of approach, which basically represents an elongatin of the runway's axis.
GLIDE SLOPE: The Glide Slope provides the vertical guidance for the pilot during a landing approach. It's created by UHF transmitter containing an antenna system operating in the range of 328.6 to 335 MHz at 150 KHz spacing. The upper and lower lobes are modulated at 90Hz and 150Hz respectively.
MARKER BEACONS: Marker beacons are used to alert the pilot that an action (e.g altitude check) is needed. This information is presented to the pilot by audio and visual cues. The ILS may contain three marker beacons: inner, middle and outer. The marker beacons are located at specified intervals along the ILS approach and are identified by discrete audio and visual characteristics. All marker beacons operate on a frequency of 75 MHz.
The instrument Landing System is an internationally normalized for navigation of aircraft upon the final approach for landing. It was accepted as a standard system by the ICAO (International Civil Aviation Organization) in 1947.
ILS uses a combination of VHF and UHF radio waves.It consists of four subsystems:
- VHF localizer transmitter
- UHF glide slope transmitter
- Marker Beacons
- Approach lighting System
LOCALIZER: One of the main component of the ILS System is the Localizer which handle the guidance in the horizontal plan. Localizer is an antenna system comprised of a VHF transmitter which uses the same frequency range as a VOR transmitter (108-112 MHz) in 0.5MHz increments.
Localizer emits two directional radiation patterns. One comprises of a bearing amplitude-modulated wave with a harmonic signal frequency of 150Hz an the other one with the same bearing amplitude-modulated wave with a harmonic signal frequency of 90Hz. These two directional radiation patterns do intersects and thus create a course plane, or a horizontal axis of approach, which basically represents an elongatin of the runway's axis.
GLIDE SLOPE: The Glide Slope provides the vertical guidance for the pilot during a landing approach. It's created by UHF transmitter containing an antenna system operating in the range of 328.6 to 335 MHz at 150 KHz spacing. The upper and lower lobes are modulated at 90Hz and 150Hz respectively.
MARKER BEACONS: Marker beacons are used to alert the pilot that an action (e.g altitude check) is needed. This information is presented to the pilot by audio and visual cues. The ILS may contain three marker beacons: inner, middle and outer. The marker beacons are located at specified intervals along the ILS approach and are identified by discrete audio and visual characteristics. All marker beacons operate on a frequency of 75 MHz.
| MARKER | CODE | LIGHT | SOUND |
| OM | _ _ _ | BLUE | 400 Hz two dashes/second |
| MM | ._._._ | AMBER | 1300 Hz Alternate dot and dash |
| IM | . . . . | WHITE | 3000 Hz only dots |
APPROACH LIGHTING SYSTEM: An approach lighting system or ALS, is a lighting system installed on the approach end of an airport and consisting of a series of lightbars, strobe lights, or a combination of the two that extends outward from the runway end. ALS usually serves a runway that has an instrument approach procedure (IAP) associated with it and allows the pilot to visually identify the runway environment and align the aircraft with the runway upon arriving at a prescribed point on an approach.
Modern approach lighting system are highly complex in their design and significantly enhance the safety of aircraft operations, particularly in conditions of reduced visibility.
Modern approach lighting system are highly complex in their design and significantly enhance the safety of aircraft operations, particularly in conditions of reduced visibility.
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