What feature must be determined for VOR to establish station passage?

To establish station passage while navigating using a VOR (VHF Omnidirectional Range), the key feature to determine is when the TO-FROM indicator shows FROM. This indicates that the aircraft has just passed over the VOR station and is now moving away from it.

When the TO-FROM indicator reads "FROM," it signifies that the aircraft has crossed directly over the VOR signal, which is pivotal in an instrument approach or navigation procedure. This moment is crucial for a pilot to know, as it affects navigation decisions, such as switching to a new waypoint and ensuring proper route adherence.

While centering the Course Deviation Indicator (CDI) is an important aspect of navigation, it does not specifically indicate station passage, since the CDI can center at other points along the course before actual passage. The cruise altitude is unrelated to this determination, and the range indicator rising pertains to distance to the VOR, which is not an indicator of passage. Hence, the correct understanding is that the "FROM" indication confirms the aircraft's position relative to the VOR station after having crossed it.