What happens immediately after establishing the RNAV/LPV/VNAV on autopilot?

After establishing the RNAV/LPV/VNAV on autopilot, pressing the APP button is the correct action to take. This activates the approach mode of the autopilot, allowing the aircraft to properly follow the lateral and vertical guidance provided by the RNAV approach. The APP mode is specifically designed to engage the autopilot for precision approaches, enabling it to capture and track both the lateral and vertical paths during an approach to landing.

Selecting APP is crucial as it prepares the aircraft to transition seamlessly through the approach phases, ensuring that it adheres to the prescribed descent path and maintains the correct course toward the runway. This step enhances the accuracy and safety of the approach, as it leverages the advanced navigation capabilities inherent in the RNAV/LPV/VNAV systems.

While other actions, such as pressing NAV, adjusting altitude settings, or switching to manual control, may be relevant in different contexts during flight, they do not directly follow the establishment of the RNAV/LPV/VNAV on autopilot in the same manner that engaging the APP mode does. This makes activating the approach mode the critical next step in maintaining optimal control and guidance during such precision approaches.