Accident Summary
An aircraft was observed maneuvering at low altitude, trailing white smoke and producing rough, erratic engine sounds. A private pilot reported that the interior of the aircraft was filled with white smoke. The aircraft then made a steep turn, pitched nose up, rolled inverted, and descended nose down to impact.
Investigation
Examination of the wreckage revealed a fractured coupling flange on the left intermediate exhaust pipe. The flange was subjected to metallurgical analysis, which determined that the fracture resulted from multiple origin fatigue failure. No other contributing factors were identified in the investigation.
Examination Findings
The fractured coupling flange exhibited characteristics consistent with fatigue cracking originating from multiple points. The metallurgical examination confirmed that the failure mode was fatigue, with no evidence of other material defects or overload. The accident sequence suggests that the exhaust system failure may have led to the observed smoke and engine irregularities, though the precise relationship between the fracture and the loss of control was not established in the source material.