This specification establishes the requirements for power operated hydraulic servoactuators when used in flight control systems. These servoactuators may be controlled by mechanical, hydraulic or electrical inputs or combinations thereof, and may be powered by one or more hydraulic systems. The complete servoactuator package may incorporate primary components such as control servovalve, input linkage and position feedback lever in addition to the actuating cylinder. Secondary components may also be included such as stability and control augmentation actuators, bypass valves, residual pressure compensators, electrohydraulic servovalves, filters, pressure switches, motor or solenoid operated shut-off valves, thermostatic control valves, hydraulic logic, mechanical locking devices and electrical transducers.