SOLUTION

Auto-pilot for an aircraft is a closed-loop system.

• Autopilots use gyroscopes to detect changes in the flight path.
• Any attitude change is sensed by a rate gyroscope which processes and produces an output signal proportional to the rate of change.
• A controller compares the actual altitude with the required altitude with the help of a feedback system.
• If there is a difference between the altitude then the controller computes a corrective signal and sends it to the servo which moves the appropriate flight control and feeds back its position to the controller. As the original attitude is gradually restored, the gyroscope output and error signal are gradually removed and the controller the pitch command. Thus this system is called a closed-loop system that needs feedback to work.