Incident Overview
While the pilot was adjusting the powerplant and propeller controls, the engine unexpectedly accelerated. Simultaneously, oil covered the windshield, obstructing the pilot's view. The aircraft subsequently descended into a bean field and flipped over during the landing.
Engine Disassembly Findings
A detailed disassembly of the engine was conducted following the accident. Examination of the rear counterweight assembly revealed the trailing pin to be worn and galled. Additionally, the sleeves in both the rear crankshaft and the counterweight exhibited signs of wear and galling. The rear counterweight leading pin also showed evidence of wear and galling spots. All propeller bolts were found to have failed in the area of the bolt head.
Conclusion
The accident sequence involved an uncommanded engine acceleration and a sudden loss of forward visibility due to oil contamination on the windshield. The subsequent forced landing in a bean field resulted in the aircraft overturning. The mechanical condition of the engine components, including worn counterweight pins and failed propeller bolts, was identified during post-accident inspection.