Definition
The imaginary line down the exact middle of a published navigation course, such as a localizer beam, VOR radial, or RNAV/GPS course. It represents zero lateral deviation — the precise track the aircraft is intended to fly along that course.
Plain English
The middle of the path you are supposed to follow. If you are right on the course centerline, you are not drifting left or right of where the course is taking you.
Context Anchor
Seen during instrument navigation and approach flying, especially when comparing the airplane’s position to the desired path shown by the instruments.
Derivation
Course comes from an older word meaning “a running” or “a path followed.” In aviation, it means the path an aircraft is meant to follow. Centerline means the line through the middle, so course centerline means the middle of that intended path.
Why Pilots Care
Remaining on the course centerline keeps the aircraft aligned with the runway or airway and clear of obstacles during low-visibility operations.
Intuition Check
Do not think of “course” as a school class here. In this term, course means the path the aircraft is supposed to follow, and the centerline is the middle of that path.
Example Sentence 1
The needle was centered, showing the aircraft was tracking right along the course centerline.
Example Sentence 2
The localizer signal provides guidance along the course centerline until the runway environment becomes visible.