VHF omnidirectional range

VHF Omni Directional Radio Range (VOR) is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine their position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons. It uses frequencies in the very high frequency (VHF) band from 108 to 117.95 MHz. Developed in the United States beginning in 1937 and deployed by 1946, VOR is the standard air navigational system in the world, used by both commercial and general aviation. By 2000 there were about 3,000 VOR stations around the world including 1,033 in the US, reduced to 967 by 2013 with more stations being decommissioned with the widespread adoption of GPS.