Stands for Non-Directional Beacon. An aerial navigation facility which simply broadcasts its station identifier in morse code. Two aerials (one in the front of the aircraft and one in the rear - or at least as differently-located as possible) receive the signal. The phase difference between the two signals is computed and displayed as a bearing from the station.

NDB stations, like VOR stations, only provide position line information. See also DME.

A major limitation of NDBs is that they only provide relative bearing information (the needle simply points to the station). This is quite different from a VOR, which shows an actual position line to or from the station, and deviation from it.

Navigating to or from an NDB is difficult for exactly this reason, because the pilot must calculate a wind correction angle and then maintain an equal crab angle away from the station (believe me, this is harder than it sounds). NDBs are also very limited in their precision, since they operate at relatively low frequencies, in the band immediately below AM radio.

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