What happened
On April 6, 2002, a Piper PA 18 Super Cub, registration F-BLEY, was conducting a mountain flight training mission near the Uls altisurface in France. The flight crew, consisting of an instructor and a student pilot, departed from Luchon airfield around 10:00 AM. After performing several touch-and-go maneuvers and reconnaissance flights, the crew approached the Uls altisurface.
During the final approach, the aircraft encountered a downdraft that placed the plane below the intended glide path. The instructor took control to execute a climbing turn to the left to clear the terrain. During this maneuver, while flying over a snow-covered slope, the crew lost visual reference to external landmarks. The instructor noted that the flight controls felt "soft," and the aircraft subsequently struck a slope with significant force. The impact resulted in two injuries and heavy damage to the aircraft.
The investigation
The investigation focused on the engine's performance and the fuel system state at the time of impact. Examination of the propeller revealed that the engine was not producing power upon impact. Investigators found that the left fuel tank and the left auxiliary tank were empty, and the carburetor bowl was dry. In contrast, the right wing tank and its associated auxiliary tank still contained approximately 50 liters of fuel.
Further inquiry into the pre-flight procedures revealed that during taxiing at Luchon, the instructor had instructed the student pilot to select the right fuel tank. However, the student pilot inadvertently selected the left tank without visually verifying the selector position. This tank contained only 25 to 30 liters of fuel. Given the engine's consumption rate of approximately 30 liters per hour at 2300 RPM, the fuel was insufficient for the duration of the flight.
Findings
- The primary cause of the engine failure was fuel exhaustion resulting from a fuel management error.
- The student pilot failed to verify the fuel selector position, inadvertently utilizing a tank with insufficient reserves.
- A lack of communication regarding specific operating procedures contributed to the error; the instructor typically used only the right tank for mountain operations to keep the left tank as an emergency reserve, a procedure unknown to the student pilot.
- The student pilot did not perform a turning point or approach checklist, which could have identified the low fuel level.
- The severity of the injuries was likely exacerbated by the use of simple lap belts instead of full safety harnesses.