VORDME

VORDME, short for VOR/DME, is a ground-based aviation navigation aid that provides two types of information from a single installation: directional bearing and distance. The azimuth guidance comes from a VOR transmitter, while a DME component supplies distance to the station.

The VOR portion transmits a reference signal and a set of phase-shifted signals that allow an aircraft receiver to determine the magnetic bearing to or from the station, expressed as a radially defined azimuth. The DME portion operates with UHF interrogations and transponder replies to measure the time delay between transmission and reception, translating this into a distance in nautical miles. The distance is a slant range, meaning it is affected by altitude and terrain and is most accurate within the line of sight of the facility.

VORDME installations are often co-located with VOR antennas at airports or along airways, and many are combined with TACAN to form a VORTAC, which also provides military channel information. In civil aviation, VOR/DME networks support en route navigation, terminal procedures, and VOR/DME approaches, offering pilots a reliable means to determine position and follow prescribed routes in instrument meteorological conditions.

Limitations of VORDME include dependence on line of sight, potential outages, and environmental factors that can affect signal quality. Although satellite-based navigation and modernized airspace concepts have reduced reliance on traditional VORs, VORDME remains a foundational and widely used navigation aid, valued for its robustness and as a backup to GNSS-based systems. See also VOR, DME, VORTAC, TACAN.