As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PROPELLER GOVERNOR WOULD NOT DECREASE BELOW 2500 RPM. AFTER REACHING CRUISE ALTITUDE, THE CREW WAS UNABLE TO DECREASE THE ENGINE RPM BELOW 2500 RPM. SHORTLY THEREAFTER THE RPM BEGAN TO 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 TEAR DOWN REPORT. IF ANY ABNORMALITY IS REPORTED WE WILL FORWARD THIS INFORMATION TO THE FAA.