Definition
A ground-based, low- or medium-frequency radio transmitter that radiates a signal equally in all directions, used as a navigation aid by aircraft equipped with an Automatic Direction Finder (ADF). The aircraft's ADF receiver senses the bearing to the station, and the pilot uses that bearing to navigate to or from the beacon, fly approaches, or identify position fixes.
Plain English
A simple radio station on the ground that sends out a signal in every direction. An aircraft receiver locks onto that signal and shows the pilot which direction the station is from the airplane, so the pilot can fly toward or away from it.
Context Anchor
Seen in instrument navigation, especially when using an automatic direction finder or when flying older procedures based on an NDB.
Derivation
Called 'nondirectional' because the transmitter sends its signal outward in all directions equally, rather than along a defined course or radial like a VOR. The work of figuring out direction is done by the aircraft's receiver, not the ground station.
Why Pilots Care
It supplies a basic navigation reference for tracking to or from a known point during approaches or en route segments, especially when other aids are limited.
Analogy
An NDB is a little like a lighthouse that shines in every direction. The lighthouse does not tell you a route by itself, but if you can see where the light is coming from, you can work out where the lighthouse is.
Intuition Check
Nondirectional does not mean the pilot gets no direction information. It means the beacon itself does not aim its signal in one direction; the airplane’s receiving equipment determines the direction to the beacon.
Example Sentence 1
The pilot tuned and identified the NDB before commencing the approach.
Example Sentence 2
During the missed approach, the crew tracked outbound from the NDB to re-enter the holding pattern.