What happens if an aircraft deviates from the VNAV path?

When an aircraft deviates from the VNAV path, the autopilot system is designed to monitor the flight's adherence to the planned vertical profile. If a deviation occurs, the autopilot can initiate corrective actions to realign the aircraft with the intended trajectory. This means that if the aircraft climbs or descends outside of the programmed path, the autopilot may adjust the aircraft's pitch and power settings to guide it back onto the VNAV path, effectively maintaining the desired altitude constraints and vertical speed.

This functionality is essential for managing an aircraft's flight path efficiently, ensuring compliance with air traffic control instructions and enhancing safety by preventing large deviations that could lead to unsafe flight conditions. It allows for a more automated and precise flying experience, thereby assisting pilots in maintaining the correct course during the vertical phase of flight.