Definition
A ground-based, low- or medium-frequency radio transmitter that radiates a signal equally in all directions. Aircraft equipped with an Automatic Direction Finder (ADF) receiver use the signal to determine the bearing from the aircraft to the station, allowing the NDB to be used for navigation, position fixing, and as the basis for non-precision instrument approaches.
Plain English
A radio station on the ground that sends out a steady signal in every direction. The aircraft's onboard receiver points to the station, so the pilot always knows which direction it is from the aircraft and can fly toward it or use it as a reference.
Context Anchor
Seen in instrument flying, especially when using an aircraft direction-finding receiver for navigation or for an NDB instrument approach.
Derivation
Nondirectional means the transmitter does not aim its signal in any particular direction -- it radiates outward equally on all sides. Beacon comes from the older sense of a fixed signal used to guide travelers. Together: a fixed radio signal that can be picked up from any direction.
Why Pilots Care
NDBs give pilots a simple navigation aid, especially useful in remote areas or as a backup when other systems are unavailable.
Analogy
Think of an NDB like a radio lighthouse. The lighthouse does not point at one boat; it shines all around, and each boat uses what it sees to work out where the lighthouse is.
Intuition Check
Nondirectional does not mean the pilot gets no direction information. It means the ground station broadcasts in all directions; the aircraft equipment determines the direction to the station.
Example Sentence 1
After identifying the NDB by its Morse code identifier, the pilot tracked inbound to the station on the published approach course.
Example Sentence 2
During the approach the crew tracked the NDB signal to stay aligned with the runway.