Plain English Meaning
A needle on the cockpit's navigation instrument that tells the pilot whether the aircraft is left of, right of, or directly on the chosen track. If the needle moves to the right, the course is to the right and the pilot turns right to get back on it.
Full Definition
An instrument display, typically a vertical needle on a VOR or navigation indicator, that shows the aircraft's lateral position relative to a selected course. The needle deflects left or right to indicate which way the pilot must steer to return to the course centerline.
Context Anchor
Seen on navigation instruments and flight displays when following a selected course, flying an instrument approach, or tracking guidance from a navigation receiver.
Derivation
Course means the intended path over the ground. Deviation means departure from that path. Indicator means a device that shows a value. Together, the name describes exactly what the instrument does -- shows how far the aircraft has deviated from the course.
Why Pilots Care
It lets the pilot make precise corrections to stay on the intended path, which is essential for accurate instrument flight and safe approaches.
Intuition Check
“Course” does not mean a training class here, and it does not simply mean where the nose is pointed. It means the navigation path the pilot selected; the indicator shows left-right error from that path.
Example Sentence 1
The pilot watched the course deviation indicator drift slowly to the left and made a small heading correction to recenter the needle.
Example Sentence 2
With the course deviation indicator centered, the aircraft tracked the approach path steadily toward the runway.