Definition
A method of area navigation (RNAV) position fixing in which the aircraft's onboard navigation system determines its location by simultaneously measuring slant-range distances from two or more ground-based DME stations and computing the intersection of those distance arcs.
Plain English
The aircraft figures out where it is by measuring how far it is from two ground stations at the same time, and using those two distances to pinpoint its position.
Context Anchor
Seen in instrument procedure and area navigation discussions, especially when describing what equipment can support an RNAV departure.
Derivation
The slash between the two identical terms is shorthand for 'using two of these at once.' The notation reflects that a single DME gives only one distance — useful, but not a fix. Two DMEs give two distances, and two distances cross at a point, which is enough to locate the aircraft.
Why Pilots Care
Provides a backup or alternative to GPS for precise area navigation when satellite signals are unavailable or not authorized.
Analogy
It is like finding your spot on a map by knowing your distance from two known landmarks. One distance narrows the possibilities; two distances can place you much more accurately.
Intuition Check
DME/DME does not mean one DME reading by itself gives a full position. It means the aircraft uses distances from multiple DME stations to work out where it is.
Example Sentence 1
When GPS is unavailable, the flight management system may revert to DME/DME positioning if suitable stations are within range.
Example Sentence 2
Pilots switched to DME/DME mode when the procedure required ground-based navigation only.