What type of range does a DME provide?

Distance Measuring Equipment (DME) provides slant range distance from the aircraft to the ground station. The term "slant range" refers to the straight-line distance measured from the aircraft to the DME antenna on the ground, rather than the horizontal distance. This measurement accounts for the altitude of the aircraft as well as its horizontal distance from the station.

When flying, pilots often need to know their distance to a specific point, such as an airport or a navigational waypoint. DME uses radio signals to determine how far away the aircraft is from the DME ground station, calculating this based on the time it takes for the signal to travel to the ground station and back. Since the radio wave travels in a straight line and has to account for vertical distance as well, the resultant measurement is slant range.

This differentiates it from other types of measurements, such as vertical range, which would imply distance in only the vertical dimension; or ground range, which would refer to the horizontal distance without considering altitude.