The VNAV ensures that altitude and speed constraints are observed, speed limits at altitudes are observed, and the pilot specified vertical profile is followed. VNAV automatically commands the autopilot to set target speeds and target altitudes in order to follow the selected flight plan during various phases of flight. It captures and levels the aircraft at the flight plan altitude constraints, and begins a descent at a planned location. During the descent, the VNAV computes a geographical path to each waypoint that has an altitude constraint. If the plan has multiple altitude constraints, the descent path is automatically adjusted so the aircraft descends smoothly and accurately through each altitude at each waypoint. This allows the pilots to confidently meet altitude and airspeed restrictions along any phase of the flight. Required changes are made through the CDU if necessary. The VNAV mode is coupled with the autopilot by pressing the VNAV button on the FGP. This couples the FGS with the FMS, and steers the aircraft in accordance with the vertical portion of the flight plan.
Smooth Skies,
Dan