Plain English Meaning
A piece of equipment near the far end of the runway that tells an approaching aircraft whether it is lined up with the runway, or off to the left or right.
Full Definition
The ground-based transmitter component of a Microwave Landing System (MLS) that provides lateral (left-right) guidance to aircraft on approach. It is normally located at the stop end of the runway and emits a scanning beam that the aircraft's MLS receiver uses to determine its angular position relative to the runway centerline.
Context Anchor
Seen in instrument approach guidance, especially in discussions of MLS .