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How does autopilot work on a plane?

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Quick answer

A plane's autopilot is a control computer that holds the heading, altitude, speed or route the pilots select. It reads data from gyroscopes, air sensors and satellite navigation, calculates any error from the target, and moves the control surfaces to correct it. Pilots manage the modes, monitor progress and can disconnect it instantly.

Autopilot on a plane works by having a computer compare the aircraft's actual heading, altitude and speed with the targets the pilots set, then moving the control surfaces to correct any difference. Pilots choose the modes, monitor every change and can disconnect it instantly with a button.

Step by step

  1. Before departure, the crew enters the planned route and cruise altitude into the flight management computer.
  2. After takeoff, a pilot engages the autopilot and selects modes such as climb, heading or route following.
  3. Sensors feed the autopilot the plane's real attitude, altitude, speed and position many times every second.
  4. The computer compares those readings with the targets and calculates the control movement needed to correct errors.
  5. Servos or fly-by-wire computers move the control surfaces, while the autothrottle sets engine thrust for the chosen speed.
  6. Pilots monitor the displays, change targets when air traffic control instructs, and disconnect the autopilot whenever needed.

Key things to understand

  1. Gyroscopic inertial units, air data sensors and satellite navigation tell the computer the plane's attitude, speed, altitude and position.
  2. Pilots dial targets such as heading, altitude and climb rate, or load a full route into the flight management system.
  3. The autopilot computer continuously calculates the gap between where the plane is and where it should be.
  4. It sends commands to servos or fly-by-wire computers that deflect the ailerons, elevators and rudder to close that gap.
  5. A linked autothrottle adjusts engine thrust to hold the selected speed while the autopilot steers the flight path.

Labelled diagram

  1. Pilot targets

    Crew selects heading, altitude, speed or a programmed route on the control panel.

  2. Sensors

    Inertial units, air data probes and satellite navigation measure the plane's actual state.

  3. Autopilot computer

    Compares actual values with targets and works out the correction needed.

  4. Actuators

    Servos or fly-by-wire computers move the ailerons, elevators and rudder.

  5. Autothrottle

    Adjusts engine thrust so the plane holds the selected airspeed.

Feedback loop inside an aircraft autopilot

Real-world examples

  • On a long overnight flight from Delhi to London, the autopilot follows the programmed route across several countries.
  • In thick winter fog, a suitably equipped airliner can use autoland to touch down on a runway with very low visibility.
  • When air traffic control orders a new altitude, the pilot dials it in and the autopilot flies the climb.
  • Small private aircraft often carry a simpler autopilot that only holds wings level and a chosen heading.

Common mistake

✗ Myth: Once autopilot is on, the pilots have nothing to do and the plane flies itself.

✓ Fact: Autopilot only follows the targets and modes the crew sets. Pilots still plan the flight, talk to air traffic control, change settings, watch for faults and weather, and take over by hand when required.

People also ask

How long do pilots use autopilot?
On a typical airliner flight, the autopilot is engaged shortly after takeoff and stays on through most of the climb, cruise and descent. Pilots usually hand-fly the takeoff and often the last part of the approach and landing, though autoland is used in poor visibility. Exact practice varies by airline and conditions.
How does autopilot know where to go?
Before the flight, pilots load the route as a chain of waypoints into the flight management system. Satellite navigation and inertial sensors tell the system the plane's position, so it calculates the course to the next waypoint and passes steering commands to the autopilot, which turns the aircraft to follow it.
Can a plane fly without pilots on autopilot?
No airliner in service is certified to fly without pilots. Autopilot cannot taxi, take off, handle most emergencies, or respond to air traffic instructions on its own; it only executes targets chosen by the crew. Fully pilotless passenger flight remains experimental and is not allowed in normal operations.
Can autopilot land a plane by itself?
Yes, many airliners can perform an autoland using signals from an instrument landing system on the ground. It is used mainly in very low visibility, and the pilots must set it up, monitor it and take over if anything looks wrong.
Does autopilot fly the takeoff?
No. On airliners in service, pilots fly the takeoff by hand and usually engage the autopilot a short time after leaving the ground. The autopilot then handles climb, cruise and often the descent under the crew's direction.
How do pilots switch the autopilot off?
Each control column or sidestick has a disconnect button, and the autopilot also drops out if a pilot pushes firmly against the controls. An aural warning sounds so both pilots know they are now flying manually.
Why do planes have more than one autopilot?
Airliners carry two or three autopilot channels so a single computer failure cannot cause a bad control input. During an automatic landing, several channels run together and cross-check each other, disconnecting if they disagree.

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