As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOW OIL PRESSURE DURING FLIGHT CAUSING PROPELLER TO GO TO LOW PITCH AND EVENTUALLY FEATHER. AIRCRAFT LANDED SAFELY AND AFTER TROUBLESHOOTING PROBLEM, FOUND BROKEN SPRING IN OIL PRESSURE RELIEF VALVE. INSTALLED NEW SPRING, ADJUSTED OIL PRESSURE AND RETURNED TO SERVICE.