Definition
An aircraft system that automatically controls the airplane's flight path by sending command signals to the flight control surfaces, using inputs from the air data computer, attitude and heading sensors, and pilot-selected modes to maintain or change altitude, heading, airspeed, and vertical speed without continuous hand-flying by the pilot.
Plain English
A system that flies the airplane for you. You tell it what altitude, heading, or speed you want, and it moves the controls to make the airplane do that.
Context Anchor
Seen in avionics and instrument-system discussions, especially where air data information is sent to other aircraft systems.
Derivation
From Greek 'autos' meaning 'self' and 'pilot' from Italian 'pilota' meaning 'one who steers.' Literally a 'self-steerer' — the airplane steering itself based on the inputs the system receives.
Why Pilots Care
An autopilot reduces workload, especially during long flights or busy instrument procedures, freeing the pilot to navigate, communicate, and manage the flight. But the pilot must always know what mode it's in and what it's doing — autopilots follow what they're told, not what the pilot meant.
Intuition Check
Do not read autopilot control system as a replacement pilot. It is a control aid that follows selected modes and available aircraft information; the pilot still has to manage and monitor the aircraft.
Example Sentence 1
After leveling off at cruise altitude, she engaged the autopilot control system to hold heading and altitude while she reviewed the approach plate.
Example Sentence 2
Before engaging the autopilot, the pilot verified that the control system responded correctly to heading and altitude commands.