As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FIRST OR SECOND COMPRESSION RING BROKE CAUSING RING LANDS TO WEAR BETWEEN FIRST AND SECOND RING LAND AND THROUGH PISTON HEAD. COMBUSTION HEAT BURNED HOLE LARGER DIRECTING PRESSURE TO ENGINE CASE. THIS PRESSURE BLEW THE ENGINE OIL OVERBOARD. THIS RESULTED IN AN EMERGENCY LANDING.