Friday, July 29, 2011

INSTRUMENT LANDING SYSTEM (ILS)

An  (ILS)  Instrument Landing System is a ground-based equipment that radiates guidance information to be received by an aircraft during final approach for correct and safe landing. It is composed of ground based equipments such as transmitter, combining/dividing network, antenna and monitors systems.
ILS have three subsytem: Localizer, Glidepath/Glideslope and Marker Beacons.
 
A.The vertical plane containing the runway centerline is defined by VHF transmitter called Localizer.
B.The horizontal plane of 2 to 4º of vertical angle above the horizontal plane is defined by a UHF transmitter called the Glide slope.
C.Distance information installed on a fixed distance reference points are provided by markers.


MARKER BEACONS
Beacons are AM transmitters operating at 75 MHz located at specific points along the landing path used to designate distance away from the threshold.
Operating  Radio Frequency
  75 MHz  ± 0.01%
Modulating Frequency
  Inner  Marker (when installed) : 3000Hz
  Middle Marker: 1300 Hz
  Outer Marker: 400 Hz
Coverage
  Inner Marker (when installed) 150 m ± 50 m
  Middle Marker : 300 m ± 100 m
  Outer Marker : 600 m ± 200 m
Identification Signal
  Inner Marker (when installed): 6 dots per second continuously
  Middle Marker: Series of dots and dashes
  a. dashes keyed at a rate of 2 dashes/sec
  b. dots keyed at a rate of 6 dots/sec
  Outer Marker: 2 dashes/sec continuously
Monitoring
  Automatic Monitoring System that transmit a warning signals to  a control point    during
  a.  Failure of modulation or keying
  b. Reduction of Power output to less than 50%
 

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