To determine NDB station passage, the ADF bearing pointer will:

To determine NDB (Non-Directional Beacon) station passage, the ADF (Automatic Direction Finder) bearing pointer will swing greater than 90 degrees and stay there. This behavior occurs because as the aircraft approaches the NDB, the signal strength will begin to increase, and the bearing pointer will progressively swing towards the direction of the NDB. When the aircraft is at the NDB station itself, the pointer swings beyond 90 degrees and stabilizes as it transitions to showing a new bearing.

This phenomenon is a key component in understanding how to use ADF systems and navigate towards NDBs effectively. The critical reason the pointer jumps beyond 90 degrees is due to the way radio waves propagate and how the ADF interprets the angle of arrival of those signals, providing a clear indication that the aircraft is near or at the NDB location.

The other answer choices do not accurately describe this process. The bearing pointer becoming erratic does not reflect normal operation at station passage. ADF operation involves smooth movements, and thus erratic behavior would suggest a malfunction or interference rather than a reliable indication of passage. The pointer starting to swing refers to the initial phase of approaching the station, but it does not convey the complete behavior observed at station passage.