Each movable surface is operated by a hydraulic actuator Figure 9-2. Hydraulically powered elevator control system. Different aircraft manufacturers call units of the primary flight control system by a variety of names. The types and complexity of control mechanisms used depend on the size, speed, and mission of the aircraft. A small or low-speed aircraft may have cockpit controls connected directly to the control surface by cables or pushrods.
Some aircraft have both cable and a pushrod system.
See figure 9-1. The force exerted by the pilot is transferred through them to the control surfaces. On large or high-performance aircraft, the control surfaces have high pressure exerted on them by the airflow. It is difficult for the pilot to move the controls manually. As a result, hydraulic actuators are used within the linkage to aid the pilot in moving the control surface.