What was found
(CAN) A/C DEPARTED AT APPROX 02:00 ZULU ON APR 2 ON IFR FLT TO VANCOUVER. DURING INITIAL STAGE OF CLIMB, RT ENGINE RPM BEGAN TO FLUCTUATE & OVERSPEED. PILOTS TRIED TO CONTROL IT WITH THROTTLE & PROPELLER CONTROLS BUT WHERE UNSUCCESSFUL & CHOOSE TO FEATHER ENGINE & RETURN TO PENTICTON. UPON INSPECTION MAINT CREW DISCOVERED THAT DRIVE ON PROP GOVERNOR BROKEN. GOVERNOR HAS APPROX 800 HRS SINCE OVERHAUL. GOVERNOR REMOVED FROM ENGINE & OVERHAULED GOVERNOR INSTALLED. A/C GROUND RUN & FOUND ACCEPTABLE FOR RETURN TO SERVICE.