This study shows the importance of correct operation of controllable pitch propeller for the safety of navigation. Operation of pneumatic control of controllable pitch propeller in a ship’s power transmission system was identified. The results of the change of the actual setting value measurements of the pitch screw propeller in the function of the value of the control air pressure have been presented. Recorded differences were assigned to operational degradation of the technical state of the pitch propeller control system. They were further confronted with the relationships between the design and time of operation. Possible consequences of operating a controllable pitch propeller with such a defect, and its impact on the correct operation of a ship’s power transmission system have been outlined. Operational requirements were presente