A pitch change apparatus comprises a hydraulic actuator for angular displacement of propellers of the propeller assembly. The hydraulic actuator has a piston and cylinder arrangement which defines fine and coarse fluid chambers. Increasing the volume of the fine chamber at the expense of the coarse chamber results in angular displacement of the propellers to a finer pitch. Increasing the volume of the coarse chamber at the expense of the fine chamber results in angular displacement of the propellers to a coarser pitch. The pitch change apparatus further comprises one or more fine hydraulic lines carrying hydraulic fluid to and from the fine chamber, and a coarse hydraulic line carrying hydraulic fluid to and from the coarse chamber. The apparatus further comprises a pressure-sensing check valve which fluidly isolates the coarse chamber from the coarse hydraulic line if the pressure in the coarse hydraulic line falls below a threshold pressure.