What altitude range is dictated by the VNAV function during a flight?

The VNAV (Vertical Navigation) function is closely tied to the Flight Management System (FMS) and is designed to assist pilots in managing altitude profiles during flight. The correct response is linked to how VNAV determines altitude based on both the FMS parameters and any pre-selected altitudes set by the pilot.

When VNAV is engaged, it uses the planned route and altitude data from the FMS. This includes the waypoints in the flight plan and any altitude constraints associated with them. Additionally, pilots can set specific altitudes manually in the FMS, which further influences VNAV’s operation. Therefore, the altitude range dictated by VNAV is effectively determined by what has been programmed in the FMS and what the pilot has pre-selected. This collaborative setup allows for optimized altitude management during various phases of flight, particularly during climbs and descents.

The other options fail to capture the specific relationship between the FMS, pre-selection, and VNAV operation. "Set altitude only" limits the automation and ignores the role of FMS dictates; "All possible altitudes" implies a lack of restrictions that are typically imposed by air traffic control and performance considerations; "The lowest available altitude" does not encompass the comprehensive altitude range defined by the interaction between