Definition
A type of RNAV flight path segment defined as a circular arc of a specified radius that begins at one fix and ends at another fix, curving around a defined center point. Unlike a standard turn, an RF leg requires the aircraft to fly a precise, repeatable curved ground track at a fixed radius, which is why it is only available on aircraft with the appropriate RNAV/RNP capability.
Plain English
A curved part of a flight path where the aircraft follows an exact arc of a set radius from one named point to another, like driving along a marked curve rather than just turning when you feel like it.
Context Anchor
Seen on RNAV instrument departures, arrivals, and approaches where the published path includes an exact curved turn instead of only straight route segments.
Derivation
‘Radius to a fix’ describes exactly what it is: a path defined by a radius (distance from a center point) that ends at a fix (a named geographic point). The phrase is literal, but worth knowing because the word ‘radius’ is the operative idea — the airplane is flying around a point at a fixed distance, not just turning toward the next waypoint.
Why Pilots Care
RF legs allow precise curved paths that optimize airspace use and avoid obstacles while reducing pilot workload during complex departures.
Analogy
It is like driving around a perfectly circular traffic circle and leaving at a marked exit. You are not just turning generally toward the exit; you are staying on the circle until you reach it.
Grounding Statement
Picture the procedure drawing a smooth circular arc in the sky, and the aircraft following that arc until it reaches the named point at the end.
Intuition Check
A fix is not a repair; in aviation it is a named point used for navigation. Constant radius does not mean any smooth turn; it means the published curved path keeps the same distance from its center throughout the leg.
Example Sentence 1
The departure procedure includes an RF leg shortly after takeoff to keep the aircraft clear of rising terrain west of the airport.
Example Sentence 2
The pilot monitored the flight director while the aircraft flew the RF leg at the published radius and airspeed.