Definition
The horizontal guidance path projected by the localizer transmitter of an Instrument Landing System (ILS), aligned with the runway centerline and providing left/right course guidance to aircraft on approach.
Plain English
An invisible line in the sky, lined up with the runway, that tells the pilot whether they are left of, right of, or on the correct path to the runway.
Context Anchor
Seen during instrument approaches that use a localizer signal, including ILS and localizer-only approaches.
Derivation
From 'localize' (to fix in a particular place) plus 'course' (the path traveled). The localizer 'localizes' the aircraft onto the runway centerline.
Why Pilots Care
Remaining on the localizer course keeps the aircraft aligned with the runway centerline, reducing the risk of a runway excursion or missed approach.
Analogy
Think of it like the center line of a lane on a road. The localizer course is the line you are trying to stay centered on as you move toward the runway.
Intuition Check
Do not read course here as a training class or lesson. In this context, course means the path the aircraft is meant to follow.
Example Sentence 1
After turning final, the pilot intercepted the localizer course and tracked it inbound to the runway.
Example Sentence 2
A small deviation from the localizer course during the final segment required an immediate correction to stay aligned.