Definition
A non-directional beacon (NDB) located on the airport itself, used as the final approach fix for an NDB instrument approach procedure. Because the beacon sits on the airport, station passage over the NDB indicates arrival at or very near the missed approach point.
Plain English
A radio beacon that is physically on the airport grounds. Pilots fly toward it using their ADF needle, and passing over it means they are at the airport.
Context Anchor
Seen on NDB instrument approach procedures when the beacon is located at the destination airport rather than away from it.
Derivation
NDB stands for non-directional beacon. 'Non-directional' means the beacon sends its signal equally in all directions, so the aircraft equipment (the ADF) is what determines the bearing to it. 'On-airport' simply describes where this particular beacon is sited.
Why Pilots Care
Its location determines critical points such as the final approach fix or missed approach point, directly affecting when descent begins and how the approach is timed.
Grounding Statement
As the airplane gets close to an on-airport NDB, the direction-finding needle can swing quickly because the aircraft is passing near the radio transmitter itself.
Intuition Check
Do not read “on-airport” as meaning the beacon is on the runway or that the approach path is automatically lined up with the runway. It means the NDB transmitter is located on the airport property or airport site.
Example Sentence 1
Because this was an on-airport NDB approach, station passage over the beacon coincided with the missed approach point.
Example Sentence 2
After crossing the on-airport NDB the pilot began the missed approach climb.