As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED LOSS OF CONTROL OF PROPELLER CAUSING MOMENTARY OVERSPEED WHICH FORCED THE PILOT TO USE THE THROTTLE TO GAIN CONTROL. DISASSEMBLY OF PROPELLER REVEALED INTERNAL OIL LEAK CAUSING A HYD LOCK WITH THE BLADES AT FINE PITCH. FURTHER INVESTIGATION OF THE SEALS REVEALED FAULTY O-RING IN THE REAR OF THE HUB OF THE PROPELLER. O-RING WAS RETURNED TO THE MFG FOR THEIR ANALYSIS.