Definition
A Required Navigation Performance (RNP) capability in which the aircraft determines its position by simultaneously measuring distances from two or more ground-based DME stations, and meets a specified accuracy standard for that segment of flight without relying on GPS or other navigation sources.
Plain English
It means the aircraft can figure out where it is accurately enough for the procedure by using distances from two ground DME stations at the same time, instead of using GPS.
Context Anchor
Seen in instrument approach chart notes and equipment requirements, especially where a procedure may allow or restrict navigation based on DME/DME instead of GPS.
Derivation
DME comes from 'Distance Measuring Equipment,' a system that measures slant-range distance from the aircraft to a ground station. RNP comes from 'Required Navigation Performance,' which sets a minimum accuracy the navigation system must meet. Combining them describes a navigation method that uses two DME signals to satisfy that accuracy requirement.
Why Pilots Care
Enables aircraft without GPS to fly accurate RNAV approaches and meet air traffic control requirements for RNP routes and procedures.
Analogy
It is like finding your location on a map by knowing how far you are from two different towns. Where those distance circles meet gives your position, if the measurements are accurate enough.
Intuition Check
Do not read DME/DME RNP as just “having DME onboard.” It means the aircraft’s navigation system can use multiple DME stations together and meet the required accuracy for the procedure.
Example Sentence 1
The approach chart noted that DME/DME RNP was an acceptable means of meeting the navigation accuracy requirement for the arrival.
Example Sentence 2
Before departure the crew confirmed the navigation system could support DME/DME RNP for the arrival procedure.