Definition
The ground-based and airborne equipment that together make up an Instrument Landing System (ILS), providing precision lateral and vertical guidance to a runway. The three functional groups are: (1) guidance signals — the localizer for lateral (left/right) alignment with the runway centerline and the glide slope for vertical (up/down) descent guidance; (2) range or position information — marker beacons (outer, middle, and where installed, inner) and/or DME, indicating distance from the runway threshold; and (3) visual aids — approach lighting, touchdown zone and centerline lights, and runway lights, which support the transition from instruments to visual references at decision altitude.
Plain English
The full set of equipment that makes an ILS approach work — the radio signals that keep the aircraft lined up with the runway and on the right descent path, the markers or distance equipment that tell the pilot how far out they are, and the lights that help them see the runway as they break out of the clouds.
Context Anchor
Seen when studying, briefing, or flying an ILS instrument approach.
Derivation
Instrument Landing System describes exactly what the system does: it uses cockpit instruments to help a pilot land when outside visual references may be limited. Component comes from a Latin root meaning “put together,” which fits because an ILS is not one single device; it is several parts working together.
Why Pilots Care
Knowing the components helps a pilot recognize what guidance is available and what to expect at each stage of the approach.
Grounding Statement
In use, the ILS components work together so the pilot can stay lined up with the runway and descend at the proper angle.
Intuition Check
Do not read “components” as a casual list of any equipment near the runway. In this context, it means the specific parts that provide, support, receive, and display ILS approach guidance.
Example Sentence 1
During the approach briefing, the captain reviewed each of the ILS components for runway 27 and noted that the middle marker was out of service.
Example Sentence 2
When one of the ILS components is out of service the approach minimums usually increase.