What happened
On December 27, 2008, a Cessna 150 L, registration F-BUML, departed from Dinan for a flight to Mortagne-au-Perche. During the cruise phase, northeast of Alençon, the pilot descended from flight level 35 to 3,000 feet. Approximately 10 nautical miles from the destination, the engine began to sputter. Despite attempts to use the carburetor heat and adjustments to the throttle and mixture, the engine lost power.
While descending through 2,500 feet, the pilot identified an unobstructed field and decided to perform an emergency landing. An emergency message was broadcast on the 123.5 MHz frequency. Although the engine appeared to restart briefly at 1,80 and the pilot continued the approach, the engine eventually failed again. The pilot completed the landing by setting the mixture to idle cut-off and switching off the magnetos.
The investigation
The investigation focused on the fuel levels and the pilot's flight planning. Upon inspection of the aircraft, the right fuel tank was found to be empty, while the left tank contained 7.5 liters of fuel. The fuel system itself showed no mechanical defects or anomalies.
Investigators examined the pilot's flight planning and fuel management. The pilot had planned a round trip between Mortagne-au-Perche and Morlaix, originally calculating fuel needs based on a standard Cessna 150. Because the intended aircraft was unavailable, the pilot switched to the F-BUML, which has a larger fuel capacity. The pilot relied on a six-hour endurance figure provided by club members rather than performing an independent calculation. Additionally, the pilot noted that he had not been monitoring the fuel gauges during the flight because he found the readings unreliable.