What happened
On Saturday, July 12, at approximately 19:15, a Piper PA-19 Super Cub, registration F-BOOX, was conducting a multi-leg cross-country flight. The pilot had completed several legs starting from Villefranche-de-Rouergue, visiting various airfields including Lac de Caussanel and Langogne, before heading toward the aircraft's home base at Nancy-Essey.
Approximately ten minutes before reaching the destination, while cruising at 3,000 feet, the pilot experienced engine roughness. Upon checking the fuel gauges, the pilot noted that the right tank was at zero while the left tank showed one-quarter full. The pilot switched the fuel selector from 'both' to 'left,' which temporarily stabilized the engine RPM. However, during a left-hand turn one minute later, the engine roughness returned, forcing the pilot to perform an emergency landing in a field near Fraismasına-en-Saintois. There were no injuries and no damage to the aircraft.
The investigation
The investigation focused on the fuel system and the discrepancy in fuel consumption between the two tanks. Post-landing inspections revealed that 14 liters of fuel remained in the left tank and 5 liters in the right tank. The investigation confirmed that the engine is gravity-fed and lacks an electric fuel pump.
While the flight manual specifies a cruise consumption of 19 liters per hour and an endurance of six hours (including reserves), the pilot noted that the flying club had provided information suggesting an endurance of over six hours under all conditions. The investigation also looked into the known issue of asymmetric fuel consumption in this specific aircraft type.