ILS-Instrument Landing System basics

ILS avionic system is a approach landing navigational aids and it stands for Instrument Landing System. ILS system provides aircraft guidance for a straight flight path landing. ILS is used in Instrument Flight Rule precision approach aircrafts from Final Approach Fix until Touchdown Point. As for insuring an ideal landing, the system is based on the intersection of the runway centerline, the Localizer beam, and the GS0 beam.

ILS,Instrument Landing System

ILS works with the help of LOC-Tx, GS0-Tx and MB-Tx with following specifications:

LOC-Tx system provides alignment with the help of runway centerline. It provies horizontal guidance and operates at VHF band (108 to 112MHz) with 20 channels. Horizontal range of operation is about 40 Km.

GS0-Tx provides fix descent rate. It operates at UHF band (329 to 335 MHz) with 20 channels. Vertical range of operation is about 1Km.

MB-Tx provides indocation to crew about the specific location of the Aircraft. It provides horizontal guidance and operates in VHF band at 75 MHz.


ILS is very powerful system for landing guidance.


•  LOC and GS0 signals suffer from bending due to site as well as terrain effect.
•  The GS0 are affected by snow, airport ground moisture etc.
•  About 20 frequency channels are available for LOC and GS use.
•  maintence and installation is costly.

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