Nanak Flights Blog

Instrument Landing System – ILS


Everyone round the globe would have, at least once in their life, dreamt of flying an aircraft. Those who don’t have the guts to give it a shot, will at least want to fly in an aircraft.

No wonder, I always chose to fly in it rather than flying it. It’s just not about only directions and altitudes for flying one. It involves a lot of (indeed a lot) technological understanding before you could even sit for a course to fly.

Though I don’t believe in life after death, it would be good if we could have had Wright Brothers now.

The factor that keeps the world on its feet is “time”. Before wright brothers’ invention travelling from India to Malaysia would take 76 hours by sea and now it’s just more than a couple of hours.

One should definitely understand the importance of an aircraft and as a step to promote its importance, here we present to you the 67 year old ILS – Instrument Landing System.


ILS was widely accepted as a standard system by International Civil Aviation Organization in 1947. ILS is a board system embedded in an aircraft with a reliable and co-operative ILS ground system installed in every airport.

What does ILS do?

It is a ground based instrumental approach that provides a clear-cut guidance to an aircraft approaching a runway. This includes both the lateral and vertical guidance of the altitudes.

How does ILS work?

It uses a combination of radio signals, lighting arrays, marker beacons, VHF localizer, glide slope and few other granular subsystems, with the localizer providing lateral guidance and glide slope for the vertical.

The localizer receiver on the system board of the aircraft is used to measure the difference in the depth of modulation of two priority signals along the runway. i.e. the 90 Hz one and the 150 Hz one. When the receiver signal stays on the centerline of the radar in the cockpit, the depth of modulation would be around 20% for each of the modulating frequencies. The difference varies based on the deviation of the aircraft from the centerline.

On a lighter note, this will not be your “cup of tea” if we you are no way related with aviation stuffs J

When is ILS used?

To maintain an efficient operation at the busiest commercial airports, ILS approach is always preferred by the pilot to ensure smooth flow of traffic. Though, ILS is not used for what it was intended to be used.

The primary intention of ILS was to ensure safe landing during the likes of low-visibility, heavy snow/rain and hail etc.

Being busy with their routine, no one would really want to understand technologies that doesn’t fall under their roof. But let’s take a day-off from our routine and understand few technologies that may be of help sometime.

After all, spending some time on gaining knowledge is not going to hurt you much. Hope you got to know a bit about ILS approach.


The next time you fly, look for the lighting arrays, marker beacons and the localizers and spread a word of mouth about the information you have gained today J J