Definition
The fixed distance, in nautical miles, from a DME station that defines a curved flight path (a DME arc) around that station. The aircraft flies the arc by maintaining this distance on the DME readout while turning continuously around the station.
Plain English
How far you stay from the DME station while flying a curved path around it. If the arc radius is 10 NM, you fly a circle around the station keeping the DME reading at 10.
Context Anchor
Seen when flying or calculating a DME arc, especially when deciding where to start a turn from the arc toward the next course.
Derivation
Arc comes from Latin arcus, meaning a bow or curve. Radius is Latin for the spoke of a wheel. Together they describe the spoke-length from the hub (the DME station) out to the curved path you fly.
Why Pilots Care
The chosen arc radius determines turn radius, groundspeed effects on lead radial placement, and the amount of airspace required to complete the maneuver safely.
Analogy
Think of walking around a pole while holding a rope. The rope length is the radius, and the path you walk is the arc.
Intuition Check
Do not confuse arc radius with the aircraft’s turning radius. Arc radius is the distance from the DME station to the arc, not the tightness of the aircraft’s turn.
Example Sentence 1
The approach chart specified a 15 NM arc radius, so the pilot maintained 15.0 on the DME while turning around the VOR.
Example Sentence 2
A larger arc radius gives more time to intercept the lead radial before turning inbound.