What function does the Autothrottle system perform?

The Autothrottle system is designed to automatically manage engine thrust during various phases of flight. This system aids pilots by adjusting the throttle settings of the aircraft's engines to maintain the desired airspeed, which enhances fuel efficiency and reduces pilot workload. By automatically regulating the engine's thrust based on predetermined settings or inputs from the flight management system, the Autothrottle contributes to smoother flight operations, especially during critical phases like takeoff, climb, cruise, and descent.

The other functions listed in the options, such as controlling auxiliary power units, managing cabin pressure, and monitoring navigational systems, relate to different systems in the aircraft. These functions are crucial for overall aircraft operation but do not pertain to the specific role of the Autothrottle system, which is focused solely on engine thrust management.