Definition
The angle, measured in degrees, between the aircraft's current heading and the inbound course of the localizer, used as the aircraft turns to join the final approach course during an ILS approach.
Plain English
The angle at which the aircraft cuts in toward the runway centerline when joining a precision approach. A small angle means a gentle join; a large angle means a sharper turn onto the course.
Context Anchor
Encountered during instrument approaches, especially when air traffic control gives a heading to join the localizer or when the pilot turns onto the final approach course.
Derivation
Intercept' comes from the Latin intercipere, meaning 'to seize between' or 'catch.' Here, the aircraft is catching the localizer beam from one side as it flies toward it, and the interception angle describes how steeply it is closing in.
Why Pilots Care
An excessively large angle can cause overshoot, beam capture instability, or a missed approach.
Analogy
It is like merging onto a road. If you enter at a gentle angle, you can blend into the lane smoothly; if you enter at a sharp angle, you may cross through the lane before you can line up with it.
Intuition Check
Do not think of it as a published angle that is always the same. It is the angle created by your aircraft’s direction compared with the localizer course at the moment you are trying to join it.
Example Sentence 1
ATC vectored the aircraft to a 30-degree localizer interception angle, which is generally considered the maximum for a clean join onto the final approach course.
Example Sentence 2
A steep localizer interception angle during the approach led to an overshoot of the final course.