As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF PILOT REPORTED AN UN-COMMANDED FEATHERING OF THE LEFT ENGINE. AFTER LANDING MAINTENANCE FOUND OIL RESIDUE ON THE OUTSIDE OF ENGINE NACELLE, AND THE TUBE ASSEMBLY FOR THE PROPELLER ACCUMULATOR CRACKED AT THE FLARE ON THE PROPELLER GOVERNOR FITTING. IT IS BELIEVED THAT THE B-NUT HAD BEEN OVER TIGHTENED ONE OR MORE TIMES, CUTTING THE FLARE OFF OF THE LINE ALLOWING OIL TO FLOW OUT.