An automatic flight control system that keeps an aircraft in level flight or on a set course, and may be directed by the pilot or coupled to a radio navigation signal is called:

• A. Autopilot
• B. Stability augmentation system
• C. Flight director
• D. Auto-throttle

Answer: (A)

The main idea is an automatic flight control system that actively manages the airplane’s attitude and flight path. An autopilot is designed to keep the aircraft in level flight or follow a set course, and it can be commanded directly by the pilot or linked to navigation signals so it flies the aircraft along a specific route or approach. It uses actuators to move the control surfaces and, in more advanced setups, can couple to navigation aids to maintain course or altitude automatically.

Stability augmentation systems improve the aircraft’s natural stability and handle some dynamic inputs, but they don’t by themselves maintain a specific flight path or level flight. A flight director provides cues to the pilot about how to fly but doesn’t move the controls on its own. Auto-throttle manages engine power to hold a selected airspeed but does not automatically steer the aircraft or hold a course.

So, the system described is autopilot.