The complexity and weight of mechanical flight control systems increases considerably with the size and performance of the aircraft. Hydraulic power overcomes these limitations. Initially only partially boosted systems were used where the pilot could still feel some of the aerodynamic loads on the surfaces.

The hydraulic circuit has hydraulic pumps, reservoirs, filters, pipes, valves and actuators. The actuators are powered by the hydraulic pressure generated by the pumps in the hydraulic circuit. The actuators convert hydraulic pressure into control surface movements. The pilot's movement of a control causes the mechanical circuit to open the matching servo valve in the hydraulic circuit. The hydraulic circuit powers the actuators which then moves the control surfaces.

This category also includes the Tornado Stick Force Sensors.