What happened
On January 20, 2008, a Flight Design CT 180 ultralight, identified as 33-WR, was conducting a cross-country flight from Libourne to Saint-Gaudens. During the flight, the pilot observed that the left wing tank was depleting faster than the right tank. After visiting Saint-Gaudens and turning back toward Libourne, the pilot noted via transparent fuel gauges that the left tank held approximately ten liters, while the right tank held about twenty-five liters.
As the aircraft approached the area near La Réole, the left tank became empty, leaving roughly ten liters in the right tank. Based on a cruise consumption of twelve liters per hour, the pilot believed sufficient reserves remained and continued the flight. Approximately ten minutes later, while performing a right-hand turn to align with runway 04, the engine lost power. The pilot attempted to restart the engine without success and performed an emergency landing on a vineyard path. During the landing roll, the left wing struck a pole, causing the aircraft to ground loop. The aircraft was destroyed, and there were two occupants on board.
The investigation
The investigation focused on the fuel system design and the pilot's management of the fuel imbalance. Investigators examined the gravity-fed fuel system, noting that each wing tank features a single fuel pickup located at the wing root. The investigation established that the pilot had experienced asymmetric fuel consumption on previous flights but had never operated the aircraft with one tank completely empty while the other contained a low volume of fuel.
Findings
- The engine failure was caused by the interruption of fuel flow to the engine.
- The fuel system design failed to adequately account for the effects of asymmetric flight; when one tank is empty, fuel in the remaining tank can shift away from the pickup point during maneuvers.
- The fuel system design did not sufficiently consider the impact of asymmetric flight on the fuel pickup location.
- There was a lack of critical information in the pilot's manual regarding the potential consequences of flying with an empty tank and an asymmetric fuel load.