Definition
The angle, measured in degrees, between the aircraft's heading and the desired course or track it is attempting to join. A larger intercept angle closes the distance to the course more quickly; a smaller intercept angle results in a more gradual join.
Plain English
How sharply you are turning toward the line you want to fly. A bigger angle gets you onto the line faster; a smaller angle eases you onto it more gently.
Context Anchor
Used in instrument navigation when joining and tracking a selected course, such as when following a radio navigation signal or turning onto an approach course.
Derivation
From Latin intercipere, 'to seize between' — to catch something on its path. The intercept angle is the angle at which you catch the course you want to fly.
Why Pilots Care
It determines how quickly and smoothly the aircraft joins the intended track without overshooting.
Analogy
It is like merging onto a road. If you approach almost parallel to the road, the merge is smooth but slow. If you cut across sharply, you get there faster but may swing past where you meant to be.
Intuition Check
Do not think of “intercept” as simply crossing a course. In this context, the goal is to meet the course at a chosen angle and then turn to follow it.
Example Sentence 1
ATC cleared the pilot to intercept the localizer, and she chose a 30-degree intercept angle to join the final approach course smoothly.
Example Sentence 2
A shallow intercept angle allowed a smooth capture of the desired track.