Definition
A type of RNAV flight path defined as a constant-radius circular arc between two fixes, anchored to a defined center point. The aircraft tracks a precise curved ground path of fixed radius, rather than flying straight between waypoints or executing a pilot- or autopilot-judged turn.
Plain English
A curved section of an RNAV route or procedure where the aircraft must follow a specific arc of a specific size, like driving along a curved road of known shape rather than cutting across in a straight line.
Context Anchor
Seen on RNAV departure, arrival, and approach procedures when the published route includes a required curved turn instead of only straight segments.
Derivation
RF stands for Radius-to-Fix. 'Radius' indicates the path is a curve of fixed distance from a center point, and 'to-Fix' means the curve ends at a defined waypoint. The name describes exactly what the leg is: a curved path of known radius ending at a fix.
Why Pilots Care
Allows precise curved routing in instrument procedures without ground-based navigation aids, supporting terrain clearance and efficient airspace use.
Grounding Statement
Picture the route as a smooth published curve that must be followed, not as a turn the pilot can freely adjust by feel.
Intuition Check
RF does not mean radio frequency here. In this term, RF means radius to fix: a curved path that ends at a specific navigation point.
Example Sentence 1
The departure procedure includes an RF leg around the ridge to the south, so the crew confirmed the aircraft was certified for radius-to-fix navigation before accepting the clearance.
Example Sentence 2
On the approach the aircraft flew the RF leg to smoothly align with the final approach course from a lateral offset.