Aircraft flight control system

An aircraft flight control system connects pilot inputs or computer commands to mechanisms that change the aircraft’s attitude, direction, and flight path.

Primary flight controls: The controls that directly change an aircraft’s pitch, roll, and yaw. Elevators, ailerons, and rudders provide the basic axes of aircraft control.
Aircraft principal axes: The three reference axes—longitudinal, lateral, and vertical—used to describe aircraft rotation. They define the rotations that flight controls produce.
Mechanical flight control system: A system that transmits pilot control inputs to surfaces through mechanical linkages. It contrasts with electronic command paths that can reshape pilot inputs.
Autopilot: An aircraft system that automatically controls flight parameters such as heading, altitude, or route. It sends commands through the flight-control system to maintain or change the aircraft’s path.
Aircraft stability: An aircraft’s tendency to return toward or remain in an equilibrium state after a disturbance. Control systems can augment stability that the airframe does not provide naturally.
Control surface: A movable aerodynamic surface that changes airflow and forces on an aircraft. Deflecting these surfaces creates the moments that alter aircraft attitude.
Pitch: Rotation of an aircraft about its lateral axis, raising or lowering its nose. Elevator commands primarily change pitch.
Fly-by-wire: An electronic flight control system that transmits pilot commands through electrical signals. Its computers can provide control laws and protections absent from purely mechanical systems.
Trim tab: A small adjustable surface that reduces the force needed to hold a primary control surface in position. Trim relieves sustained pilot effort during steady flight.
Redundancy (engineering): The use of duplicate components or paths so a system can continue functioning after a failure. Flight controls use independent channels and backups to preserve command capability.

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