As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE OVERSPEED DUE TO INTERNAL FAILURE OF THE PROPELLER GOVERNOR. SPOOL B-3166 SEPARATED FROM SPOOL EXTENSION A-3167, CAUSING GOVERNOR TO ACT AS IF IN AN UNDERSPEED CONDITION, SENDING BOOST OIL PRESSURE TO FORCE PROPELLER TO LOW PITCH. SEPARATION MAY HAVE BEEN CAUSED BY LOSS OF SPRING PIN B61320250.