VOR system
The tail knows
The antenna on the tail of your aircraft knows something. And it is pretty important. It receives signals from nearby VOR (very high frequency omnidirectional range) ground stations.
The VOR system consists of a ground component and an aircraft receiver component. Ground stations transmit radio signals on a designated frequency. On your aircraft, there’s a VOR antenna, a VOR frequency selector, and an in-cockpit instrument. The instrument can be an course deviation indicator (CDI), horizontal situation indicator (HSI), or radio magnetic indicator (RMI). At VOR/DMEs, distance measuring equipment (DME) collocates with a VOR to give distance from the VOR station.
The ground station is referenced to magnetic north and emits two signals. These are a 360-degree sweeping signal and an omni-directional reference signal. The signals are compared at the aircraft’s receiver and the difference between them is displayed in the cockpit. The instrument in the cockpit looks like a compass. Centering the needle shows the radial the airplane is on, giving the direction from the station.
There are three classes of VORs: terminal, low-altitude, and high-altitude. Terminal VOR signals reach up to about 12,000 feet high and a radius of 25 nautical miles. Low-altitude VORs are usable up to about 18,000 feet high and 40 nm. High-altitude VORs may be usable up to 60,000 feet high and 130 nm.
The FAA is phasing out some VORs (in favor of GPS), but there are still hundreds of VOR stations around the country. If you get lost, they can quickly help identify your position. They might be 1940s technology, but it’s nice to know you can always find your way home.
