VORs

VOR, short for VHF Omnidirectional Range, is a ground-based radio navigation aid used by aircraft. A VOR station transmits signals that allow a receiver in an airplane to determine its position relative to the station by determining a magnetic bearing, or radial, from the station.

Operation: The VOR ground facility emits a reference signal in all directions and a second signal whose phase rotates with direction. The onboard VOR receiver compares the rotating signal with the reference and computes the aircraft's bearing to the station. The instrument display can show a selected radial or course to be flown, and pilots can intercept or track a specified radial.

Applications: VORs are used for en-route navigation, to follow airways defined by VOR radials, and to execute instrument approaches. A position fix can be obtained by crossing radials from two or more VOR stations. When a VOR is co-located with DME or TACAN, it provides distance information as well (VOR/DME or VORTAC).

Coverage and limitations: VOR signals are line-of-sight and range varies with altitude, transmitter power, and terrain. Typical ranges are tens to a couple hundred nautical miles. Signals can be degraded by interference, multipath, or station outages. VORs provide azimuth information but not distance (distance is provided by DME in combined systems).

Status and context: VOR technology has been largely complemented by GPS-based RNAV, but VOR systems remain integral to conventional IFR navigation and serve as a regulatory backup and a survivable source of bearings in case of GNSS outages. The network includes VORs, DMEs, and VORTACs globally; maintenance and calibration ensure accuracy.