Definition
A curved flight path flown at a constant distance from a DME (Distance Measuring Equipment) station, used as a course on instrument approach procedures. The aircraft maintains a fixed nautical-mile distance from the station while turning around it, joining the final approach course at a specified point.
Plain English
A flight path shaped like part of a circle, flown by keeping a steady distance from a ground navigation station. Instead of flying a straight line, the pilot curves around the station at the set distance until reaching the point where the approach turns inbound to the runway.
Context Anchor
Seen on the plan view of instrument approach charts, where an arc connects one charted path or point to another while keeping a set distance from a station.
Derivation
DME stands for Distance Measuring Equipment, a system that tells the pilot how far the aircraft is from a ground station. 'Arc' comes from the Latin arcus, meaning 'bow' or 'curve' — the same root as 'arch.' Together it means a curved path defined by a constant DME distance.
Why Pilots Care
Allows precise navigation and positioning for an approach without radar vectors from air traffic control.
Analogy
Think of being on the end of a rope tied to a pole. If you walk while keeping the rope tight at the same length, you trace a curve around the pole. A DME arc works the same way — the DME distance is the rope, and the station is the pole.
Intuition Check
Do not read “arc” as just a curved line printed on the chart. In this context, it is a specific path the pilot flies by keeping a set DME distance from a navigation station.
Example Sentence 1
The approach chart showed a 15 DME arc from the station, so the pilot turned to keep the distance steady at 15 nautical miles until intercepting the final approach course.
Example Sentence 2
After reaching the arc, the crew began a descent while maintaining the published distance from the station.