Definition
An RF (Radius-to-Fix) leg is an RNAV path segment defined as a constant-radius circular arc between two fixes, curving around a defined center point. The leg is fully specified by its terminating fix, the center of the arc, and the radius, allowing the aircraft to fly a precise, repeatable curved ground track. RF legs require aircraft and avionics specifically authorized for RF capability and are commonly used in RNP approach and departure procedures where terrain, airspace, or obstacles demand a tightly controlled curved path.
Plain English
It is a curved section of a flight path shaped like part of a circle. The aircraft flies around a fixed point at a fixed distance, so the turn follows the same exact curve every time.
Context Anchor
Seen in instrument procedure design and on procedures that require the aircraft’s navigation system to fly a precise curved path.
Derivation
‘Radius-to-Fix’ describes exactly what the leg does: the aircraft flies a fixed radius around a center point, ending at a named fix. The name itself tells you the geometry — a radius, terminating at a fix.
Why Pilots Care
Allows the aircraft to make precise, repeatable turns that maintain obstacle clearance and meet procedure design requirements.
Analogy
Think of a car following a roundabout at a steady distance from the center pole. The radius stays the same all the way around, so the curve is smooth and predictable.
Intuition Check
Do not read “leg” here as a straight section of a route. An RF leg is still one route segment, but this particular segment is curved.
Example Sentence 1
The approach included an RF leg that curved the aircraft around rising terrain before joining the final approach course.
Example Sentence 2
The aircraft followed the RF leg to intercept the final approach course exactly at the fix.