Definition
A radius-to-fix (RF) leg is a curved flight path segment defined by a fixed radius arc between two waypoints, with the arc centered on a defined point. Unlike a standard turn where bank angle and ground track depend on wind and pilot technique, an RF leg requires the aircraft to track a precise circular path of specified radius, ending at a named fix. RF legs are used in RNP procedures where terrain, airspace, or obstacle avoidance demands repeatable, predictable curved tracks.
Plain English
A curved part of a flight path that follows a set arc — like flying along a circle of a specific size — between two points on a charted procedure. The aircraft must stay on that exact curve rather than just turning roughly toward the next point.
Context Anchor
Seen on some RNAV and RNP instrument approach procedures where the charted path must curve precisely around terrain, airspace, or other constraints.
Derivation
From radius (the distance from the center of a circle to its edge) and fix (a defined geographic point in navigation). The name describes the leg literally: a path of fixed radius ending at a fix.
Why Pilots Care
RF legs allow safe, repeatable curved paths around terrain or obstacles and support noise abatement while maintaining required navigation accuracy.
Analogy
Think of following a curved lane on a road that ends at a particular sign. You are not just turning generally toward the sign; you are staying on the marked curve all the way to it.
Intuition Check
Do not read an RF leg as “turn toward the next point whenever convenient.” It is a published curved path with a set shape that must be followed to the fix.
Example Sentence 1
The approach into the valley uses an RF leg to keep the aircraft clear of rising terrain on the south side of the airport.
Example Sentence 2
After the RF leg the aircraft rolled out precisely on the final approach course for the RNP runway.