What happened
Shortly after departing the airport, the aircraft began to emit smoke and subsequently caught fire. The pilot attempted to return to the departure airfield but was unable to maintain altitude as the engine lost power. The aircraft impacted a heavily wooded state park.
The investigation
Investigators recovered the wreckage and examined the engine components. They found that the exhaust pipe for cylinder number five had separated from the assembly. Notably, this specific pipe showed no signs of burning or soot accumulation, indicating it detached prior to the fire spreading extensively through the engine compartment. Extensive melting was observed around the intake and exhaust ports on cylinder five, and the head of this cylinder was completely burned through.
Records indicated that the aircraft had undergone an annual inspection just 30 hours before the accident. During that service, the exhaust system gaskets had been replaced. To determine the cause of the separation, a metallurgical examination using a scanning electronic microscope was performed on the failed exhaust pipe flange. The analysis revealed no evidence of nut-tightening marks on the flange where it should have been secured. In contrast, distinct nut-tightening marks were observed on two other exhaust pipes that remained attached to the engine.
Findings
The primary mechanical failure was the separation of the cylinder five exhaust pipe. The lack of tightening marks on the failed component, compared to the marked bolts on the remaining pipes, suggests improper installation or retention during the recent maintenance. This failure likely led to a loss of engine power and subsequent fire, preventing the pilot from returning to the airport.