Definition
A type of curved flight path used in RNAV (area navigation) procedures, defined as a constant-radius arc between two waypoints, centered on a specified point. The aircraft's flight management system flies the curve precisely, maintaining the defined radius from the center fix until reaching the termination waypoint.
Plain English
A pre-planned curved turn between two points on a route. Instead of flying straight from one waypoint to the next, the aircraft flies a smooth, exact arc — like tracing part of a circle — with the curve's size and shape already built into the navigation database.
Context Anchor
Seen on some instrument departure, arrival, and approach procedures, especially procedures designed for precise satellite-based navigation.
Derivation
The name describes exactly what defines the path: a fixed radius (distance from a center point) leading to a fix (a named waypoint where the curve ends). Naming the path by its geometry helps pilots and designers understand that the curve is mathematically defined, not flown by feel.
Why Pilots Care
Allows precise curved paths that fit complex airspace or terrain while maintaining obstacle clearance.
Analogy
It is like following a painted curved lane on a road that leads to a marked intersection. You are not just aiming at the intersection; you are staying in the curved lane until you reach it.
Intuition Check
Do not read Radius-To-Fix as simply “turn toward the fix.” It means a published curved segment with a set radius that must be followed to the fix.
Example Sentence 1
The approach into the mountain airport included a Radius-To-Fix leg that curved the aircraft around rising terrain before lining up with the runway.
Example Sentence 2
The pilot maintained the published radius during the Radius-To-Fix segment to remain within protected airspace.