Definition
A radio navigation system that measures the slant-range distance in nautical miles between an aircraft and a ground station. The aircraft transmits an interrogation signal to the ground station, which replies; the airborne equipment calculates distance based on the time elapsed between the interrogation and the reply.
Plain English
A piece of equipment in the aircraft that talks to a ground station and tells the pilot how many nautical miles they are from it.
Context Anchor
Seen on instrument charts, approach procedures, and cockpit navigation displays when a pilot needs to identify position by distance from a radio navigation station.
Derivation
The name states its function directly: equipment that measures distance between the aircraft and a ground station using radio signals.
Why Pilots Care
Accurate distance information supports position awareness, timing of flight segments, and safe execution of instrument approaches.
Grounding Statement
If the DME display reads 12.0 NM, the aircraft is 12 nautical miles in a straight line from the selected DME station.
Intuition Check
DME does not measure how far the airplane has flown along its path. It measures straight-line distance from the aircraft to the selected DME station.
Example Sentence 1
Cleared direct to the VOR, the pilot watched the DME count down as the aircraft approached the station.
Example Sentence 2
During the approach briefing, the crew noted the DME distance at which to begin the descent.