Definition
A precision approach system that provides pilots with horizontal and vertical guidance to a specific runway. It uses radio signals — a localizer for left/right alignment with the runway centerline, and a glideslope for the correct descent angle — together with marker beacons or distance-measuring equipment to indicate progress along the approach.
Plain English
A ground-based radio system that guides an aircraft down to a runway when the pilot can't see it well, by showing whether the plane is left or right of the runway centerline and whether it's too high or too low on the descent path.
Context Anchor
Seen on instrument approach charts, in avionics frequency setup, and in air traffic control clearances such as being cleared for an ILS approach.
Derivation
Straightforward English: an Instrument Landing System is a system that lets the pilot land using cockpit instruments rather than outside visual references. The name describes the function directly.
Why Pilots Care
It allows a safe landing when visibility is too low for a visual approach, preventing diversions and reducing the risk of controlled-flight-into-terrain accidents.
Intuition Check
An ILS does not automatically land every airplane. It provides precise guidance; the pilot or approved autopilot still has to fly that guidance correctly.
Example Sentence 1
Tower cleared us for the ILS approach to runway 9 with a 300-foot ceiling and one mile visibility.
Example Sentence 2
ATC cleared the flight for the ILS approach to runway 09 and requested a report at the outer marker.