Definition
A type of RNP turn defined by a fixed radius arc between two waypoints, allowing the aircraft to follow a precise, repeatable curved path regardless of wind or groundspeed. Known in RNP procedure design as a Radius-to-Fix (RF) leg, the flight management system maintains the specified radius to the turn's terminating fix.
Plain English
A turn that follows a fixed-radius curve along the ground, like tracing a section of a circle. The aircraft holds the same distance from the center of the turn the whole way around, instead of drifting wider or tighter as wind or speed changes.
Context Anchor
Seen in RNP instrument approach procedures, especially where the published path must curve around terrain, obstacles, or restricted airspace.
Derivation
Constant means unchanging; radius is the distance from the center of a circle to its edge. So a constant radius turn is one where that distance stays the same throughout the turn — producing a clean, circular arc instead of an irregular curve.
Why Pilots Care
Allows aircraft to stay within protected airspace and meet strict accuracy requirements during instrument approaches.
Analogy
Imagine driving on a circular highway off-ramp. The curve has a built-in shape — you don't decide where to turn, you just follow the arc. A constant radius turn does the same thing in the air.
Grounding Statement
Picture the airplane following a smooth slice of a circle rather than making a loose, changing turn from one straight line to another.
Intuition Check
Do not read “constant” as meaning the airplane keeps the same bank angle or speed. Here it means the size of the curved path stays the same.
Example Sentence 1
The RNP approach included a constant radius turn around the ridge, keeping the aircraft clear of terrain on both sides.
Example Sentence 2
The procedure specified constant radius turns around the waypoint to avoid terrain.