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In combination with a controllable pitch propeller and means for driving the same, hydraulic means for automatically changing the blade angle of said propeller, valve means for controlling said hydraulic means, a governor actuated pilot valve for adjusting said valve means in response to the speed of said propeller driving means to cause said driving means to drive said propeller at substantially constant speed, and manual means operatively associated with said valve means having three operative positions, one of which is a neutral position for maintaining said hydraulic means under the control of said governor actuated pilot valve, the other two of which are control positions for rendering said governor actuated pilot valve ineffective and controlling said valve means to maintain the propeller in a condition of positive high or low blade angle independently of the action of said governor.