Plain English Meaning
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.
Full 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.
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.