What was found
PROPELLER GOVERNOR WOULD NOT DECREASE BELOW 2500 RPM. AFTER REACHING CRUISE ALTITUDE, CREW WAS UNABLE TO DECREASE THE ENGINE RPM BELOW 2500. SHORTLY THEREAFTER THE RPM BEGAN TO GRADUALLY INCREASE ON ITS OWN. ENGINE WAS FEATHERED TO PREVENT PROPELLER OVERSPEED. THE NR 1 PROPELLER GOVERNOR FAILED TO CONTROL. WE WILL SEND THE PROPELLER GOVERNOR TO O/H AND REVIEW THE TEARDOWN REPORT. IF ANY ABNORMALLY IS REPORTED WE WILL FORWARD THIS INFORMATION TO FAA.