What condition identifies positive station passage?

Positive station passage occurs when an aircraft has successfully passed over a VOR (VHF Omnidirectional Range) station and is now receiving the signal from the opposite direction. This condition is most accurately identified by the first positive, complete reversal of the TO-FROM indicator on the aircraft’s navigation display.

When flying toward the VOR station, the TO indicator shows that the aircraft is "going to" the station. As the aircraft reaches the station, the TO-FROM indicator will switch from "TO" to "FROM," indicating that the aircraft is now "coming from" the station. This reversal is a precise and reliable way to confirm that the aircraft has crossed over the VOR.

The other options, while they mention important aspects of VOR navigation, do not specifically denote positive station passage. The first visible indication of the station on the HSI relates more to proximity rather than the confirmation of crossing over it. Meanwhile, the successful activation of the VOR signal simply indicates that the system is operational and does not confirm the aircraft's position relative to the station. Lastly, the moment the DME (Distance Measuring Equipment) locks onto the station provides distance information but does not confirm the directional passage over the station. Thus, the correct and