DME: Distance Measuring Equipment
Distance Measuring Equipment (DME) are ground-based navigation aids used by aircraft.
The signals transmitted between the aircraft and the ground DME beacon allow the aircraft to accurately determine the distance separating it from the beacon. DME is used at an airport or en route and is one of the primary navigation aids in air route systems.
DME equipment measures the distance between an aircraft and a ground station by timing the propagation delay of radio signals in the frequency band between 960 and 1215 megahertz (MHz). A line of sight is required between the aircraft and the ground station.
A common combination is a DME located with a VHF omnidirectional range (VOR) transmitter at a single ground station. When this occurs, the frequencies of the VOR and DME equipment are paired. This setup allows an aircraft to determine its azimuth angle and distance from the station.
Low-power DME transponders are also associated with some instrument landing system (ILS) installations, ILS locators, and microwave landing systems (MLS). In those situations, the pulse spacing/frequency of the DME transponder is also paired with the ILS, LOC, or MLS frequency.
