Definition
A ground-based, low or medium frequency radio transmitter that radiates a signal equally in all directions. An aircraft equipped with an Automatic Direction Finder (ADF) receives the signal and displays the bearing from the aircraft to the station, allowing the pilot to track to or from the beacon.
Plain English
A radio station on the ground that sends out a signal in every direction at once. A receiver in the aircraft points an arrow at the station, so the pilot knows which way it is.
Context Anchor
Seen on navigation charts, approach charts, and in radio navigation discussions, especially with older or backup navigation equipment.
Derivation
‘Nondirectional’ means ‘not aimed in any particular direction.’ Unlike a VOR, which sends out information that lets the aircraft work out a specific radial, an NDB just transmits a steady signal outward in all directions — the aircraft equipment does the work of figuring out which way the station lies.
Why Pilots Care
Provides reliable navigation in areas lacking VOR coverage and serves as a backup during GPS outages or for certain instrument approaches.
Intuition Check
Nondirectional does not mean the pilot gets no direction. It means the ground station does not aim the signal; the aircraft equipment works out the direction to the station.
Example Sentence 1
After passing the final approach fix, the pilot tracked inbound to the NDB and began the descent to the minimum descent altitude.
Example Sentence 2
When flying the published approach, the crew used the NDB to confirm position along the final course.