What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On may 17, 2017 at 20:32 local time, a Stinson 108-2 experienced an engine failure that led to a loss of power and in-flight fire. The aircraft was substantially damaged during the forced landing in a tree. FAA investigator arrived on scene within hours of forced landing. Aircraft was observed leaking fuel from several tanks. Engine showed large hole in crankcase indicative of a catastrophic failure. Bottom surface of aircraft had fabric covering burned away for several feet aft of firewall. Fuel selector, mixture control and magnetos were off. Airworthiness inspector arrived next day, took additional pictures that revealed the middle cylinder on co-pilots side had separated, with a bent connecting rod, missing piston and missing exhaust valve. The cylinder and case break exhibited damage consistent with catastrophic overload. The inside of the cylinder exhibited damage consistent with a broken valve being forced into the cylinder head repeatedly. The piston, piston rings, piston pin and exhaust valve head were not able to be located at the scene. Engine was disassembled at salvage yard by NTSB and FAA officials. Upper half of exhaust valve stem found still lodged in guide. Large amounts of free play existed between stem and guide, evidence of excessive wear. Pushrod shroud and pushrod of subject valve both bent. Valve failed midway up stem and had fallen into cylinder and jammed piston, causing entire cylinder assembly to be broken off crankcase. The subject cylinder was not one of the two that had been removed and replaced at last annual. While the engine could not be turned, the magnetos and carburetor did not have any visual defects or evidence of failure.
As the FAA filed it
ON MAY 17, 2017 AT 20:32 LOCAL TIME, A STINSON 108-2 EXPERIENCED AN ENGINE FAILURE THAT LED TO A LOSS OF POWER AND IN-FLIGHT FIRE. THE AIRCRAFT WAS SUBSTANTIALLY DAMAGED DURING THE FORCED LANDING IN A TREE. FAA INVESTIGATOR ARRIVED ON SCENE WITHIN HOURS OF FORCED LANDING. AIRCRAFT WAS OBSERVED LEAKING FUEL FROM SEVERAL TANKS. ENGINE SHOWED LARGE HOLE IN CRANKCASE INDICATIVE OF A CATASTROPHIC FAILURE. BOTTOM SURFACE OF AIRCRAFT HAD FABRIC COVERING BURNED AWAY FOR SEVERAL FEET AFT OF FIREWALL. FUEL SELECTOR, MIXTURE CONTROL AND MAGNETOS WERE OFF. AIRWORTHINESS INSPECTOR ARRIVED NEXT DAY, TOOK ADDITIONAL PICTURES THAT REVEALED THE MIDDLE CYLINDER ON CO-PILOTS SIDE HAD SEPARATED, WITH A BENT CONNECTING ROD, MISSING PISTON AND MISSING EXHAUST VALVE. THE CYLINDER AND CASE BREAK EXHIBITED DAMAGE CONSISTENT WITH CATASTROPHIC OVERLOAD. THE INSIDE OF THE CYLINDER EXHIBITED DAMAGE CONSISTENT WITH A BROKEN VALVE BEING FORCED INTO THE CYLINDER HEAD REPEATEDLY. THE PISTON, PISTON RINGS, PISTON PIN AND EXHAUST VALVE HEAD WERE NOT ABLE TO BE LOCATED AT THE SCENE. ENGINE WAS DISASSEMBLED AT SALVAGE YARD BY NTSB AND FAA OFFICIALS. UPPER HALF OF EXHAUST VALVE STEM FOUND STILL LODGED IN GUIDE. LARGE AMOUNTS OF FREE PLAY EXISTED BETWEEN STEM AND GUIDE, EVIDENCE OF EXCESSIVE WEAR. PUSHROD SHROUD AND PUSHROD OF SUBJECT VALVE BOTH BENT. VALVE FAILED MIDWAY UP STEM AND HAD FALLEN INTO CYLINDER AND JAMMED PISTON, CAUSING ENTIRE CYLINDER ASSEMBLY TO BE BROKEN OFF CRANKCASE. THE SUBJECT CYLINDER WAS NOT ONE OF THE TWO THAT HAD BEEN REMOVED AND REPLACED AT LAST ANNUAL. WHILE THE ENGINE COULD NOT BE TURNED, THE MAGNETOS AND CARBURETOR DID NOT HAVE ANY VISUAL DEFECTS OR EVIDENCE OF FAILURE.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.