What is an Instrument Landing System (ILS)?

An instrument Landing System (ILS) is defined as a precision runway approach aid based on two radio beams which together provide pilots with both vertical and horizontal guidance during an approach to land.

It uses a combination of radio signals to enable a safe landing even during challenging conditions such as low visibility.

The ILS system provides both course and altitude guidance to a specific runway. This system is used to execute a precision instrument approach procedure or precision approach. An instrument landing system (ILS) facility is a highly accurate and dependable means of navigating to the runway in IFR conditions.

The first ILS system tests began in the U.S.A. in 1929.

In weather conditions where the cloud ceiling is low and the visibility factors are bad, it enables the aircraft to approach the runway low and land safely with electronic devices.

It is the system that greatly facilitates the landing of pilots when visibility is very low, especially in foggy and snowy weather. This system is not required for airports established in flat and fog-free areas.

The airport where the ILS system will be located should have a geographical location that does not affect the broadcast performance of the system. The Signal generation area needs corrected terrain. The environmental terrain conditions of the location of the airport must be suitable.

The Instrument Landing System provides an approach path for the exact alignment and descent of an aircraft on the final approach to a runway. The pilot receives guidance information through a ground-based directional transmitter which is the localizer, providing horizontal guidance, and the glide-slope, providing vertical guidance.

ILSs are referred to as ‘Precision Approaches’ because it guides the aircraft both vertically and laterally.

How ILS Operates?

ILS works by beaming two radio transmissions of different frequencies up from the landing runway, one of 90 Hz and one of 150 Hz. A radio beacon called a localiser is normally built at the end of the runway with multiple pairs of directional antennas.

Localisers are responsible for the horizontal guidance of the aircraft. On the aircraft, an ILS receiver interprets the information and reports which side the aeroplane is situated on to allow the pilot to adjust accordingly. When both signals are overlapping, the aeroplane is flying perfectly down the centre of the course to the runway.

A glideslope antenna provides vertical guidance and operates the same as a localiser which is turned on its side. It also uses 90 Hz and 150 Hz frequencies which are interpreted by the ILS receiver on an aircraft.

ILS is a navigation assistance system that allows the aircraft to approach the runway with precision.

This is approximately 3 degrees to the horizon which gives the aircraft a descent rate of approximately 500 feet per minute. To align the aircraft to the runway centerline, the difference in depth of modulation is considered.

If all the Instrument Landing System components are available together with an approved approach mechanism, then the precision approach is executed by the pilot.


  1. This type of system approach is very accurate.
  2. It is used to help the pilot during the landing and approach of the aircraft.
  3. It helps the pilot to watch the runway and the airports when there is finite visibility.
  4. It helps to increase situational awareness and safety measures.
  5. It guides to the aircraft runway in both vertical and horizontal planes.


Due to the localized, glide slope beams moving objects, vehicles, and other big reflecting objects produces interference, this generated interference reduces the directional signal’s strength.

ILS technology has been around for a long time. It remains the most common system used today, but there have been (and are) alternatives.

Aviation technologies are developing day by day and air transport is becoming the rapidly rising star of the transportation industry. Navigation and approach systems play a significant role in the safe flight and landing of the aircraft.

Satellite technology and GPS today provide a viable alternative, and several systems have been implemented. GPS-based systems are available in several regions as support for ILS navigation.