What happened
While operating in cruise flight at 3,000 feet, the pilot of the aircraft noticed the engine began surging and observed fluctuations in the manifold pressure. Approximately 30 to 60 seconds after the surging ceased, the engine power dropped significantly, running no more than at idle power with a very rough operation, before eventually losing all power.
The pilot executed a forced landing onto a paved road. During the maneuver, the aircraft veered left off the roadway, causing the left wing to strike a small tree. The aircraft sustained substantial damage during the event.
The investigation
An inspection of the engine revealed that the connecting rods for cylinders 3, 4, and 5 had broken loose from the crankshaft. The crank journals for these three cylinders showed evidence of extreme heat.
Additionally, investigators found that the number 6 piston had a fatigue fracture across the piston crown structure, aligned with the piston pin. A hole had been burned in the piston near the center of the crown along a fracture line leading to the piston interior, originating from the crown surface. The inspection of this piston showed no material defects or surface anomalies at the origin of the larger fatigue crack, and the base metal composition was consistent with alloy AE109 specifications. At the time of the investigation, the engine manufacturer reported they were in the process of redesigning the piston used in TSIO-550-C engines.