Definition
A curved flight path flown at a constant distance from a DME (Distance Measuring Equipment) station, measured in nautical miles. The pilot maintains the specified distance shown on the DME readout while turning continuously around the station, producing a circular arc on the chart. DME arcs are commonly used as transitions from the en route structure onto an instrument approach.
Plain English
A flight path that curves around a navigation station, keeping the same distance from it the whole way. Instead of flying a straight line, you fly a circle (or part of one) around the station at a fixed range, like say 15 miles out.
Context Anchor
Seen on instrument approach charts, especially when an aircraft is guided from an arrival route or feeder route onto another part of an approach.
Derivation
DME stands for Distance Measuring Equipment, the avionics system that tells the pilot how far they are from a ground station. 'Arc' comes from the Latin arcus, meaning 'bow' or 'curve' — the same root as archery. The path forms part of a circle, hence 'arc.'
Why Pilots Care
Provides a reliable way to position the aircraft for an approach or to lose altitude without flying a straight radial, increasing flexibility and safety in instrument conditions.
Analogy
Imagine you're tied to a pole by a rope. If you walk while keeping the rope tight, your path traces a circle around the pole. A DME arc is the same idea — the DME station is the pole, and your distance reading is the rope.
Grounding Statement
On a DME arc, the DME distance should stay about the same while the aircraft’s heading gradually changes.
Intuition Check
Do not think of a DME arc as just any curved turn. It is a curved path flown at a specified measured distance from a DME station.
Example Sentence 1
ATC cleared us to intercept the 12 DME arc and fly it to the final approach course.
Example Sentence 2
ATC cleared the aircraft to fly the DME arc until established on the inbound course.