What happened
On July 21, 2004, a PZL 104 Wilga 80, registration F-GICY, was conducting a flight from Cuers-Pierrefeu to Arcachon. During the flight, the pilot noted low fuel indications and diverted to Alès to refuel. After departing Alès, approximately ninety minutes into the second leg, the pilot again observed fuel gauges approaching zero. While attempting to manage the remaining fuel by switching to the right tank, the engine lost power. Although the engine briefly restarted after the pilot adjusted the aircraft's pitch and engaged emergency pumps, the engine failed a second time approximately four nautical miles from Marmande. The pilot subsequently performed an emergency landing in a sunflower field near Gabion, Virazeil. There were no injuries and no damage to the aircraft.
The investigation
Investigators examined the fuel system and the refueling process. Post-incident measurements revealed that the total fuel capacity of the aircraft was significantly lower than the manufacturer's specification of 176 liters. The right tank held 82.85 liters, while the left tank held only 56.75 liters, totaling 139.60 liters. The investigation found that the refueling process was inconsistent; at the initial departure, the pilot added 75 liters, and at Alès, 84 liters were added. The investigation also noted that the aircraft's fuel tanks contained internal baffles, which made the final stages of refueling particularly slow. Furthermore, the pilot's flight logs indicated that previous flights had never exceeded 80 minutes, whereas the pilot believed the aircraft had an endurance of 3 hours and 20 minutes after refueling.
Findings
- The primary cause of the engine failure was fuel exhaustion due to the pilot's failure to detect the decreasing fuel volume in the tanks.
- The actual usable fuel capacity was significantly less than the manufacturer's stated capacity, leading to a discrepancy between the pilot's expected endurance and the actual available fuel.
- The refueling process was incomplete because the pilot relied on visual overflow rather than ensuring the tanks were filled to their true capacity, a task usually handled by a mechanic who was more familiar with the slow filling rate caused by internal baffles.