How are altitude constraints managed in VNAV?

Altitude constraints in VNAV are primarily managed through pre-programmed waypoints set in the Flight Management System (FMS). The FMS contains an extensive database of waypoints along the planned route, and each of these waypoints can have specific altitude constraints assigned to them. When the aircraft approaches a waypoint, the VNAV system utilizes this information to automatically adjust the aircraft's altitude in accordance with the constraints.

This automated process enhances flight efficiency and helps maintain safety by ensuring that the aircraft adheres to the required altitudes during various phases of the flight, such as climbs, descents, and levels of cruise. By relying on the pre-programmed data, the system can optimize vertical navigation without needing continuous input from the pilot or reliance on external instructions.

While pilot manual entry can modify certain parameters if necessary, and air traffic control might provide altitude clearances, the primary method for managing altitude constraints is through the dynamic information encapsulated in the FMS waypoints. This makes the system an integral part of modern aviation navigation, facilitating smoother and more consistent altitude management during flights.