ILS

An instrument landing system (ILS) is a radio beam transmitter that provides a direction for approaching aircraft that tune their receiver to the ILS frequency. It provides both lateral and a vertical signals. It is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow.

An instrument approach procedure chart (or approach plate) is published for each ILS approach to provide the information needed to fly an ILS approach during instrument flight rules (IFR) operations. A chart includes the radio frequencies used by the ILS components or navaids and the prescribed minimum visibility requirements.

Radio-navigation aids must provide a certain accuracy (set by international standards of CAST/ICAO); to ensure this is the case, flight inspectionorganizations periodically check critical parameters with properly equipped aircraft to calibrate and certify ILS precision.