How can pilots override VNAV guidance?

The ability for pilots to override Vertical Navigation (VNAV) guidance is fundamentally based on the use of manual control inputs or selecting alternate vertical modes. When pilots choose to use manual control inputs, they effectively take charge of the aircraft's vertical flight path, allowing them to climb, descend, or level off as they see fit, without being constrained by the automated VNAV commands.

Additionally, selecting alternate vertical modes gives pilots a way to modify the aircraft's vertical flight path while still utilizing some aspects of the autopilot system. This means that even when VNAV is engaged, pilots have the flexibility to switch to other modes that may be more appropriate for the specific circumstances they are encountering, such as following a specific altitude constraint or responding to ATC instructions.

While activating the autopilot system and changing the flight plan in the Flight Management System (FMS) can influence the flight profile, they do not directly provide a mechanism for overriding VNAV guidance. Disengaging all navigation systems would be an extreme measure and is not a common practice for overriding VNAV, as it would also disengage other essential navigational functions. Thus, using manual control inputs or alternate vertical modes is the most effective method for pilots to manage VNAV guidance when necessary.