What happened
During cruise flight, the pilot experienced engine backfiring and a loss of power that left only idle thrust available. Unable to maintain altitude or reach a suitable airfield, the pilot executed an emergency landing on the frozen surface of the Yokon River. The impact caused the aircraft to nosed over.
The investigation
A post-accident examination of the airplane and its engine revealed a critical maintenance discrepancy. The carburetor float bowl drain plug was found to be missing from the assembly and could not be located on the wreckage or in the surrounding area. This omission allowed fuel to leak from the carburetor, leading to the power loss observed during flight.
Findings
The aircraft had received an annual inspection just 1.5 hours of flight time prior to the accident. The absence of the drain plug indicates a failure in the pre-flight or post-maintenance inspection process. The lack of fuel flow due to the open drain hole resulted in fuel exhaustion and the subsequent forced landing.
Safety message
Maintenance personnel must verify that all drain plugs and access panels are securely installed after servicing. Pilots should perform thorough pre-flight inspections, including checking for signs of fuel leaks or missing components, especially shortly after maintenance has been performed.