Definition
The role of Distance Measuring Equipment (DME) in providing the pilot with a continuous, accurate readout of slant-range distance in nautical miles from the aircraft to a selected ground station. The airborne DME unit transmits paired pulses to the ground station, which replies on a separate frequency; the unit measures the time between transmission and reply and converts it to distance, typically also displaying groundspeed and time-to-station along the current track.
Plain English
DME tells the pilot how far the aircraft is, in nautical miles, from a chosen ground station. It does this by sending out radio pulses, timing how long the reply takes to come back, and turning that time into a distance.
Context Anchor
Seen in instrument flying when using navigation stations or procedures that include DME distance, such as identifying a fix, checking progress, or following an instrument approach.
Derivation
Function comes from a Latin word meaning performance or carrying something out. In this context, it means what the equipment is meant to do: provide distance information to the pilot.
Why Pilots Care
It supplies accurate distance data required for position awareness, timing fixes, and compliance with instrument procedures.
Analogy
DME is like asking, “How far am I from that point?” and getting the straight-line answer, not the road distance or ground-track distance.
Grounding Statement
If you fly directly over a DME station at altitude, the display may still show a small distance because it is measuring the diagonal line from the aircraft down to the station.
Intuition Check
Function does not mean a button or a math operation here. It means what DME does for the pilot: it provides distance from the selected station.
Example Sentence 1
Crossing the 15 DME arc, the pilot turned inbound on the published approach course.
Example Sentence 2
Knowing the function of DME helped time the turn onto the final approach course.