Which of the following is a key function of the autopilot system?

The key function of the autopilot system is flight path control. Autopilot systems are designed to automatically control the aircraft's trajectory and maintain specific flight parameters, such as altitude, heading, and speed, without pilot input. This capability allows pilots to manage the aircraft more efficiently, reducing workload, especially during long flights or in busy airspace.

While navigation is a component of autopilot functionality, the system's primary role is to control the flight path. It can be integrated with navigation systems to enhance its performance, but the essence of autopilot is to maintain the desired flight path as set by the pilot. Communication management and weather monitoring, though important functions in aviation, fall outside the primary duties of an autopilot system, which is specifically focused on controlling flight dynamics.