When does VOR and VOR/DME station passage occur?

VOR and VOR/DME station passage occurs when the aircraft crosses the VOR or VOR/DME station, which is indicated by the TO-FROM indicator changing to FROM. This means that the aircraft has effectively passed the station and is now moving away from it, rather than towards it. The TO-FROM indicator serves as a critical navigational reference, helping pilots determine their position relative to the VOR station.

As the aircraft approaches the station, the indicator will switch from TO (indicating the aircraft is on a course towards the station) to FROM (indicating that the aircraft has passed the station and is now heading away). This transition is a definitive sign of station passage, making it an essential aspect of navigating with a VOR or VOR/DME system.

The other options, while related to navigation, do not accurately describe the specific moment of passage. The crossing of the radial occurs in conjunction with station passage but does not directly indicate it. Similarly, the indication of TO suggests an approach to the station, and distance decreasing refers to the approach phase, not the passage itself.