What happened
On May 18, 1999, a Cessna 152, registration F-GJCO, departed Toussus-le-Noble for Mimizan. Approximately 15 nautical miles from the destination, the pilot experienced a loss of engine power followed by engine misfires. Realizing the fuel supply was depleted, the pilot performed an emergency landing in a field near Pissos. While the engine remained operational upon touchdown, the nose wheel sank into the soft ground, causing the aircraft to flip onto its back. The aircraft sustained damage during the incident.
The investigation
The investigation focused on the fuel levels and the pilot's flight planning. Upon inspection, the left wing tank was found to be empty, while the right tank contained a small amount of fuel. The aircraft's tachometer indicated a total flight time of 3 hours and 30 minutes since startup.
According to the aircraft's flight manual, the total fuel capacity is 98 liters, with 93 liters of usable fuel. At a cruise speed of 100 knots and 4,000 feet, the recommended fuel consumption is 23 liters per hour, provided a lean mixture is used. The pilot's flight plan calculated a required fuel load of 92.59 liters, which included a 10% contingency, a 20-minute reserve, and allowance for taxiing. This calculated amount was just within the usable limit of the aircraft.
Findings
- The pilot performed the flight using a rich mixture throughout the cruise phase rather than the recommended lean setting.
- The failure to adjust the mixture resulted in a higher fuel consumption rate than the 23 liters per hour used in the initial calculations.
- The flight planning was erroneous as it did not account for the increased consumption caused by the rich mixture setting.