What happened
On September 9, 2002, at approximately 14:00, a SOCATA MS 235 F Rallye, registration F-GNHL, was performing glider towing operations near Saint-Auban. Approximately five minutes after takeoff, while climbing in a right-hand turn at an altitude of roughly 1,250 meters, the engine power decreased significantly, with the RPM stabilizing at approximately 1,500.
Upon being notified of the engine failure via radio, the glider pilot immediately released from the tow. The pilot of the towing aircraft attempted to troubleshoot the engine failure but was unsuccessful. As the aircraft lost altitude, the pilot considered returning to the Saint-Auban aerodrome but ultimately decided to perform a forced landing in a nearby field.
Following advice from other pilots in the vicinity, the pilot targeted a large field and initially planned a north-facing approach. While executing a right-hand turn toward the landing site, the pilot realized the approach would result in a tailwind. In an attempt to reposition for a headwind landing, the pilot initiated a left-hand turn, during which the intended landing zone was lost from view. The aircraft continued on its course toward the field but was at too low an altitude to correct the trajectory. The aircraft struck the top of a tree, entered a ground loop, and came to rest in a hedge, causing significant damage to the nose gear, propeller, and flaps.
The investigation
The investigation focused on the fuel system and the accuracy of fuel quantity information. Examination of the wreckage revealed that the left fuel tank contained approximately 90 liters of fuel, while the right tank contained only about 0.25 liters. No leaks were found in the fuel lines or tanks, and a small amount of fuel remained in the carburetor bowl.
The pilot stated that visual fuel level checks were not possible in this aircraft type and that the gauges were imprecise. Consequently, the pilot relied on the aircraft's refueling log, which indicated a total fuel quantity of 150 liters. During the flight, the pilot had performed four consecutive towing operations, all while using the right fuel tank.
Findings
- Inadequate fuel management led to the depletion of the right fuel tank.
- The refueling logs provided inaccurate information regarding the distribution of fuel between the tanks, as they only listed a total quantity without specifying the amount in each tank.
- The aircraft's logbook lacked updated information regarding fuel additions made during the three hours of flight preceding the accident.
- The pilot's troubleshooting actions during the engine failure were rushed, specifically the brief five-second switch to the left tank before switching back to the right.