What is the vertical mode for LNAV once established on autopilot?

When the autopilot is engaged in LNAV (Lateral Navigation) mode, the vertical mode that is typically associated with maintaining altitude is the VPTH, or Vertical Path. This mode helps to manage the altitude in relation to a predefined vertical profile, particularly when flying along an air traffic control clearance or a flight plan. Once the airplane is established in LNAV, it will use both lateral and vertical path information to guide the aircraft along the flight path as required.

In this context, VPTH is specifically focused on maintaining the vertical profile rather than simply managing the vertical speed or glide slope (which is handled in different modes). By using VPTH, the aircraft ensures that it adheres to the planned altitude constraints efficiently while still following the course set by the LNAV.

The other options, while related to vertical navigation, do not represent the correct vertical mode for LNAV in autopilot operation. For instance, vertical speed (VS) focuses solely on how fast the aircraft is climbing or descending and may not follow a specific path or altitude target, whereas a glide slope (GS) is involved in precision approaches and not used in the general scenario of LNAV mode. Similarly, VGP (Vertical Guidance Path) is not a standard term typically used