Full-regime automatic flight control systems (AFCS) consist of at least a flight director (FD) and an autopilot (AP). “Full regime” means the AFCS has enough modes to control the aircraft from after takeoff to short final. It also means the AP controls the trim to operate over the full airspeed and centerof- gravity envelope. Selecting different modes and resetting the altitude preselector will be required during the flight, but you can leave the AP engaged throughout the flight.
The FD computes what to do and the AP servos provide some muscle to move the control surfaces. But the real muscle, like with the human pilot, comes from the autopilot using trim to keep control forces from becoming excessive.
