As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE RPM DROPPED FROM 2200 TO 1900 DURING CRUISE. UNABLE TO CONTROL RPM ON LEFT ENGINE AFTER RPM DROP. PROP FEATHERED ON GROUND WHEN SHUTTING DOWN ENGINE. MAINTENANCE DISCOVERED THE NUMBER ONE ENGINE PROP GOVERNOR HAD SHEARED THE DRIVE SHAFT FOR THE PROP GOVERNOR. PROP GOVERNOR WAS REPLACED AND CHECK FLIGHT WAS SATISFACTORY. POST FLIGHT OIL FILTER/SCREEN INSPECTION WAS SATISFACTORY.