Incident
A pilot reported hearing a muffled explosion from the engine compartment during flight. The engine subsequently quit, and flames emerged from the engine cowling. The cabin began filling with smoke, and oil spewed onto the windscreen. The pilot successfully executed procedures for in-flight fire and smoke in the cockpit, then performed an emergency landing in a field.
Landing and Gear Collapse
Before landing, the pilot delayed gear extension to remain clear of obstructions and reach a suitable landing area. The gear did not have enough time to fully extend, and it collapsed on touchdown.
Examination Findings
An examination of the airplane revealed that the dual magneto had separated from the engine. The bottom magneto hold-down clip was found in the cowling, but neither the lockwasher nor the nut were recovered. The bottom surface of the magneto housing exhibited two longitudinal markings (chipped paint). The bottom clip had spacing that matched the chipped paint on the magneto housing, suggesting the clip had moved longitudinally relative to the housing.
Examination of the top magneto housing flange, which had separated from the magneto, revealed fracture surface markings indicative of fatigue cracking before the onset of overstress separation.