Definition
An airborne and ground-based radio navigation system that measures the slant-range distance in nautical miles between an aircraft and a fixed ground station. The aircraft's DME interrogator sends paired pulses to the ground transponder, which replies on a different frequency; the equipment calculates the time between transmission and reply and converts it into a distance reading displayed in the cockpit.
Plain English
A radio system that tells the pilot how many nautical miles the aircraft is from a specific ground station. The aircraft sends a signal, the ground station answers, and the equipment turns the round-trip time into a distance shown on a display.
Context Anchor
Seen on navigation displays, instrument procedures, and position reports when a pilot needs distance from a navigation station.
Derivation
The name simply describes the function — equipment that measures distance. No deeper origin is needed.
Why Pilots Care
Gives precise distance to waypoints or airports, which is required for many instrument procedures, holding patterns, and fuel planning.
Intuition Check
Do not assume DME distance is the same as ground distance on a chart. DME shows straight-line distance from the aircraft to the station, so it can read slightly higher when you are close to the station and above it.
Example Sentence 1
Approaching the VOR, the pilot watched the DME count down from 15 to 10 nautical miles before beginning the descent.
Example Sentence 2
We cross-checked our position by comparing the DME distance with the GPS readout.