Definition
A named geographic point that defines the center of a circular flight path on an RNAV procedure, around which the aircraft flies an arc of a specified radius. It is the reference point for path computations on Radius-to-Fix (RF) legs and DME arc legs.
Plain English
It is the point in the middle of the circle that the aircraft is flying around. The aircraft stays a set distance from this point as it flies the curve.
Context Anchor
Seen in instrument procedure coding and path-and-terminator leg discussions, especially when a procedure contains a curved path.
Derivation
Center comes from an older word meaning the middle point of a circle. Fix, in navigation, means a known position on the earth. Together, center fix means the known position used as the middle point for building a curved path.
Why Pilots Care
Correct identification ensures the FMS or autopilot flies the exact arc needed for obstacle clearance and procedure compliance.
Analogy
If you draw a circle with a compass, the sharp point stays at the center while the pencil draws the curve. The center fix is like the sharp point; the aircraft flies the curve, not the center point.
Intuition Check
Do not assume a center fix is a fix located in the middle of your route. Here, it means the fixed point used as the center of a curved flight path.
Example Sentence 1
The RF leg on the approach was built around a center fix two miles north of the final approach course, giving the aircraft a smooth curving turn onto final.
Example Sentence 2
Before departure the pilot verifies that the center fix is correctly loaded in the navigation database for the RF segment.