Plain English Meaning

The moment the aircraft stops navigating by tuning ground stations and starts navigating by GPS-defined points stored in the flight computer.

Full Definition

The point in flight at which the aircraft's primary means of navigation changes from conventional ground-based navigation aids (such as VOR, DME, or NDB) to Area Navigation (RNAV), in which position is computed from satellite signals (GPS) and/or other multi-sensor inputs rather than from tracking signals to or from a specific ground . The involves a procedural and change: the selects the on the navigation , verifies the , and follows a defined by computed rather than by or bearings to a station.