A propeller hydraulic actuation system, includes a double-acting dual chamber hydraulic pitch change actuator. The pitch change actuator includes a first pressure circuit having first fluid supply lines and a first hydraulic chamber and a second pressure circuit having second fluid supply lines and a second hydraulic chamber. A piston separates the first and second chambers. At least one pressure sensor is provided for obtaining pressure measurements from which a load differential (F) applied to the piston by the circuits can be calculated. A closed loop controller is arranged to control the fluid supplied to the first and second pressure circuits, wherein the closed loop controller includes an actuator position loop arranged to utilise feedback on the actuator position to control the actuator position.