Plain English Meaning

The aircraft figures out where it is by measuring how far it is from two ground stations at the same time, and keeps refreshing that fix as it flies along.

Full Definition

A method by which an RNAV system continuously refines its computed position by simultaneously measuring slant-range distances from two or more ground-based DME (Distance Measuring Equipment) stations and triangulating the aircraft's location from those measurements.

Context Anchor

Seen in RNAV departure discussions, especially when the aircraft’s navigation system may use ground-based distance signals instead of GPS to keep its position accurate.

Derivation

DME stands for Distance Measuring Equipment, a system that measures distance by timing pulses between the aircraft and a ground . 'Updating' here means refreshing the 's position fix — using two DME distances together gives a single on the map, the way two tape measures from known walls would pin down a spot on the floor.