Aircraft flight controls are the means by which a pilot controls the direction and attitude of an aircraft in flight.
Flight control systems are subdivided into what are referred to as primary and secondary flight controls. Primary flight controls are required to safely control an aircraft during flight and consist of ailerons, elevators (or, in some installations, stabilator) and rudder. Secondary flight controls are intended to improve the aircraft performance characteristics or to relieve excessive control loading, and consist of high lift devices such as slats and flaps as well as flight spoilers and trim systems.
B727 Flight Control Surfaces. Source: Wikicommons. Origin: FAA(USA)
Movement of any of the primary flight controls causes the aircraft to rotate around the axis of rotation associated with the control surface. The ailerons control motion around the longitudinal axis (roll), the elevator controls rotation around the lateral axis (pitch) and the rudder controls movement around the vertical axis (yaw).
The most basic flight control systems are mechanical and, although they date back to the earliest aircraft types, are in use in the majority of light, general aviation aircraft. In this design, a collection of mechanical components such as cables, pulleys, rods and chains transmit the movement of the flight deck controls to the appropriate control surface(s). In larger and faster aircraft, the aerodynamic forces become too great for the pilot to overcome without assistance so hydraulic systems are often incorporated to move the flight control surface. In some newer aircraft models, the quest for reduced weight and the associated fuel savings has led designers to replace most of the mechanical components with computers and fiber optics to produce control systems which are referred to as Fly-By-Wire.