What Is an ILS Approach?

Decades ago, airplanes started to get more and more automated than ever. The result is a rise in safety on and off the ground. Autopilot was a system that was already installed on several large airplanes over the years but the introduction of ILS has changed how many see airports and landings. What exactly is ILS?

Photo Credits: ONUR

What is an ILS?

ILS (Instrument Landing System) is a system which is a radio navigation aid that directs the aircraft towards the runway for landing. In simpler words, it acts like a glide path or an automated route that the aircraft follows while landing and safely touches the ground. It shows the pilots if they are at the correct height for the approach and how far left or right the aircraft is from the runway centerline. Originally, it allows an aircraft to approach until it is 200 feet (61 m) over the ground, within a ​1⁄2 mile of the runway. In the majority of the cases, the ILS provides an accurate and precise signal that allows the plane to land itself. This system is most useful when it is cloudy or visibility is extremely poor, as it allows the pilots to fly the aircraft down to the runway, even if they only manage to see the runway in the final few seconds.

Photo Credits: Pilot Stories

How does it work?

It is used to help provide lateral and vertical guidance to the pilots when landing an aircraft. The ILS works by sending two directional radio signals, the localizer (108 to 112 MHz frequency), one of them telling the pilots if they or high or low and the other one telling them if they are left or right of the runway centerline. The relationship between the aircraft’s position and these signals is displayed on an aircraft instrument, often additional pointers in the attitude indicator. The ILS receiver on the aircraft measures the difference in depth of modulation (DDPM) between the signals. The radio beam signals are interpreted by the aircraft’s computer systems and relay this information to the pilots. The pilots are then able to make corrections to the aircraft’s flight path to ensure it remains in-line with the runway and descends at the correct rate. More often the pilots only need to trim the aircraft to the path. Either the autopilot can fly the approach, or it can be manually flown by the pilots. In some conditions, such as when it’s very foggy, only the autopilot can land the aircraft as the pilots would not have sufficient time and clear vision to see the runway and react if they only saw the runway at the last second.

Photo Credits: Encyclopedia Britannica

Types of ILS

ILS’s are categorized into 3 types. CAT I, CAT II, and CAT III. A Category III approach allows the autopilot to land the aircraft itself, however, a CAT I approach requires the pilot to land the aircraft. ILS’s aren’t available at all airports, some airports have other navigation aids available to help guide the aircraft, but these are less accurate which restricts the weather in which the pilots can land. ILS’s tend to be utilized regardless of how far the pilots can see the runway due to their accurate guidance. They can be used to facilitate an approach and enhance the flight crew’s situational awareness. Such systems are rapidly increasing as years pass by to improve safety for everyone.

Photo Credits: Gold Coast Airport


  • https://www.flightdeckfriend.com/ask-a-pilot/what-is-an-ils-approach/
  • https://altigator.com/ (Cover photo)

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