As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED A LOSS OF ENGINE RPM CONTROL (RUNAWAY PROP). AFTER REPLACING THE PROPELLER GOVERNOR AND THE PROPELLER THERE WAS STILL NO PROP CONTROL. MAINTENANCE FURTHER INVESTIGATED THE PROBLEM AND FOUND THE PROPELLER GOVERNOR DRIVE SHAFT GEAR SHEARED. AFTER ENGINE TEAR DOWN, IT WAS FOUND THAT A “BODY, HYDRAULIC TAPPET P/N 72877 WAS ALSO BROKEN. IT US UNKNOWN WHETHER THIS IS THE CAUSE OF THE ENGINE OVER SPEED OR THE PROPELLER GOVERNOR DRIVE SHAFT.