How does an ILS work?

by Captain Joe

How does an ILS work? One of the most ask question regarding how an airplane flies towards the runway without any visual aids.

So the Instrument landing system is a ground based radio navigation system giving pilots a lateral and vertical guidance towards the runway as they are in approach in IMC (Instrument Meteorological Conditions).

To fly an ILS approach, the aircraft has to be fitted with an adequate ILS receiver to display and converted the picked up signals on the cockpit instruments. Besides that, you need the necessary ILS approach chart with important data like ILS frequency and identifier code, ILS inbound course and glide slope angle, given minimum descent altitudes or heights depending on the ILS category, and last but not least the go arround procedure.

The so called localizer is an antenna array normally located beyond the end of the runway and generally is built up of several pairs of directional antennas. They send out radio signals in the horizontal axis of the runway.(This is very often mistaken, as many airports have to Localizer antennas, for either direction of the runway. So this plane right here is not flying in regards to this antenna right here, but to the antenna at the far end of the runway it´s landing on)

Also important to know, at the same time the localizer transmits the so called ILS facility identification code. What is that good for? Because the frequency range for the ILS is fairly small, you could pick up the wrong ILS frequency of a nearby airport. Therefor each ILS sends out it´s own morse code, for example the ILS identification code for John F.Kennedy airport runway 04Right is IJFK, which will be displayed in our ILS receiver instrument or you have to actually listen to the morse code and compare it to the one on your ILS approach chart. Please comment below what type of plane you´re flying if you still have to self tune the ILS frequency and listen to the morse code.

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