What happened
The aircraft experienced a complete loss of engine power while en route, necessitating an emergency forced landing. Approximately one hour and thirty minutes into the flight, the pilot first noticed signs of engine roughness. This was followed by a temporary spike in oil temperature, which quickly returned to normal levels.
About one hour later, the situation deteriorated further with a twenty-five RPM decrease in engine speed accompanied by continued roughness. Throughout the subsequent half-hour, engine RPM continued to drop steadily. In an effort to restore power, the pilot leaned the fuel mixture and cycled the carburetor heat on and off. Despite these interventions, total power loss occurred, forcing the pilot to initiate a forced landing. To avoid obstacles during the touchdown, the pilot intentionally ground looped the aircraft.
The investigation
Post-accident examination of the engine revealed no evidence of mechanical failure or malfunction that would have caused the power loss. The physical condition of the engine components was consistent with normal operation absent external interference.
Findings
Meteorological data and icing probability charts indicate that the existing conditions were conducive to carburetor ice formation. The ambient temperature was recorded at 70 degrees Fahrenheit, while the dew point was 55 degrees Fahrenheit. This specific combination of temperature and dew point creates a high risk for moisture accumulation within the carburetor, leading to ice buildup that restricts fuel-air flow and causes engine roughness or failure.
Safety message
Pilots must remain vigilant regarding carburetor ice risks even in warm temperatures. The presence of significant humidity, indicated by a narrow spread between temperature and dew point, can facilitate ice formation in the carburetor throat. Regular use of carburetor heat is essential to prevent or mitigate this hazard during flight.