An aircraft autopilot is a control system that helps a plane maintain a chosen heading, altitude, speed, or flight path. It matters because long flights require steady control for many hours, and small corrections can reduce pilot workload and improve fuel efficiency. Autopilot does not replace pilots, and it does not make decisions like a human crew.
Pilots choose modes, monitor the system, and can disconnect it at any time.
Key Facts
- Autopilot compares a target value to a measured value, then commands a correction: error = target - measured.
- Heading hold uses compass and inertial data to keep the aircraft pointed toward a selected direction.
- Altitude hold uses air pressure altitude data to maintain a selected altitude by adjusting pitch through the elevators.
- Airspeed hold or autothrottle uses speed sensors and engine thrust to help maintain a selected speed.
- Control surfaces include ailerons for roll, elevators for pitch, and rudder for yaw.
- A basic feedback idea is correction ∝ error, meaning larger errors usually require larger control responses.
Vocabulary
- Autopilot
- An autopilot is a system that automatically controls parts of an aircraft's flight according to modes selected by the pilots.
- Flight director
- A flight director shows steering cues on the cockpit display so pilots or the autopilot can follow the selected flight path.
- Servo
- A servo is a motorized actuator that moves a control surface or control linkage in response to an electronic command.
- Inertial reference system
- An inertial reference system uses gyroscopes and accelerometers to estimate the aircraft's attitude, motion, and direction.
- Mode
- A mode is a selected autopilot function, such as heading hold, altitude hold, vertical speed, or approach guidance.
Common Mistakes to Avoid
- Thinking autopilot flies with no pilot supervision is wrong because pilots select the modes, verify the flight path, and disconnect the system if needed.
- Confusing heading with course is wrong because heading is the direction the nose points, while course is the path over the ground, which can differ because of wind.
- Assuming autopilot controls only the engines is wrong because many autopilot systems move control surfaces for pitch, roll, and yaw, while autothrottle controls thrust.
- Forgetting sensor errors can affect autopilot is wrong because the system depends on accurate airspeed, altitude, attitude, and navigation data to make safe corrections.
Practice Questions
- 1 An aircraft is assigned to maintain heading 090 degrees, but its measured heading is 084 degrees. What is the heading error, and should the autopilot command a turn left or right?
- 2 A plane is set to hold 10,000 ft but climbs to 10,180 ft. If the autopilot tries to reduce the error at 300 ft per minute, about how many seconds would it take to return to 10,000 ft?
- 3 A pilot selects altitude hold, but the airspeed begins to decrease while the plane is climbing in turbulent air. Explain what the pilot should monitor and why autopilot does not remove the need for human decision making.