Definition
A ground-based, low- or medium-frequency radio transmitter that broadcasts a signal equally in all directions. An aircraft equipped with an Automatic Direction Finder (ADF) receiver uses the NDB signal to determine the bearing from the aircraft to the station, allowing the pilot to navigate to or from the beacon.
Plain English
A radio station on the ground that sends out a signal in every direction. A receiver in the aircraft picks up the signal and points to where the station is, so the pilot can fly toward it or away from it.
Context Anchor
Seen in navigation, instrument approach, chart, and NOTAM information, especially for older radio navigation procedures.
Derivation
Non-directional means the signal is not aimed in any one direction — it goes outward equally on all sides. This matters because the direction information comes from the aircraft's receiver figuring out where the signal is coming from, not from the beacon pointing anywhere.
Why Pilots Care
Serves as a backup navigation aid when GPS or VOR coverage is unavailable and supports non-precision instrument approaches.
Analogy
An NDB is like a lighthouse that sends out radio instead of light. The beacon does not point at the airplane; the airplane’s receiver figures out where the beacon is.
Intuition Check
“Non-directional” does not mean the pilot cannot get direction from it. It means the beacon sends the same signal outward in all directions; the aircraft equipment determines the direction to the beacon.
Example Sentence 1
The pilot tuned the ADF to the NDB frequency and tracked inbound to the beacon for the approach.
Example Sentence 2
In remote areas the crew used the NDB to maintain course when other navigation aids were out of range.