ILS
A ground-based radio system that guides an aircraft down to the runway on both centreline and descent path.
Also written
instrument landing system
An Instrument Landing System pairs a localizer, which defines the runway centreline, with a glideslope transmitter, which defines the descent angle — usually three degrees. The crew flies the two needles to the runway, which is what lets an airliner land in visibility far below what a visual approach needs. For a spotter, an ILS approach is the predictable one: aircraft arrive on the same line at the same angle, which is why the approach path to an ILS runway is where most arrival photographs are taken.
Nearby in Aviation
- IATA — The airline trade body whose three-letter codes appear on tickets and baggage tags.
- ICAO — The United Nations agency that sets international aviation standards, and the source of the four-letter airport codes.
- landside — The part of an airport before security, open to anyone.
- line up and wait — A clearance to enter the runway and hold in the takeoff position without a takeoff clearance.