What was found
(CAN) THE AIRCRAFT WAS IN ENROUTE, WHEN THE RT ENGINE PROPELLER RPM DROPPED, UNCOMMANDED, TO 80 PERCENT. THE PROPELLER RPM COULD NOT BE CONTROLLED, NOR COULD THE PROPELLER BE FEATHERED, AND THE RT ENGINE WAS SHUTDOWN AS A PRECAUTION. THE AIRCRAFT RETURNED TO AIRPORT WHERE MAINTENANCE FOUND THE RT PROPELLER GOVERNOR TO BE FAULTY. THE PROPELLER GOVERNOR WAS REPLACED AND THE AIRCRAFT WAS RETURNED TO SERVICE.