Accident Details
On 2 July 2015 at approximately 18:30 local time, a Piper J3C-65 Cub registered F-BFML operated by a club under general aviation and personal convenience was performing a local flight. The pilot, who held a private pilot license with 758 total flight hours (61 on type), departed from runway 05 and flew east for about ten minutes before returning to the traffic pattern for runway 05 after overflying the field.
During the final turn, the engine began misfiring, and engine speed and power decreased. The pilot manipulated the throttle and toggled carburetor heat but without effect. He announced his intention to make a forced landing and touched down in an unharvested wheat field. The aircraft rolled about 20 meters before nosing over and coming to rest inverted. The aircraft was heavily damaged.
Engine Examination
Post-accident examination of the engine and fuel system revealed no malfunctions that could have contributed to the event.
Weather Conditions
At 18:00, the METAR for Pontoise aerodrome reported variable wind at 3 knots, visibility greater than 10 km, temperature 30 °C, dew point 15 °C, and QNH 1019 hPa.
Carburetor Heat Usage
The pilot stated that he likely applied carburetor heat on downwind, following the club's checklist. Carburetor heat increases intake air temperature, reducing air density and enriching the air-fuel mixture. At high ambient temperatures, this can cause an excessively rich mixture leading to irregular engine operation and power loss. The pilot had been taught to always use carburetor heat regardless of conditions. Following the event, the club issued a directive advising pilots not to use carburetor heat when the temperature exceeds 30 °C.
Pilot Actions
The low altitude at which the power loss occurred prevented the pilot from reaching the runway or a more suitable emergency landing field. He stated that despite pulling back on the control stick, he could not prevent the aircraft from nosing over.