What happened
On July 31, 2018, a Bell 47G-2 helicopter, registration F-GVIG, was performing agricultural spraying operations near Sigean, France. The mission involved treating mosquito larvae habitats using a specialized spraying system. After completing a series of rotations, the pilot decided to treat one additional plot of land before returning to base.
While flying over the Bages-Sigean pond at approximately 350 feet, the engine suddenly lost power. The pilot attempted an autorotation to manage the descent, but due to the difficulty of judging height over the water's surface caused by sun reflections, the aircraft struck the water heavily. The impact shattered the canopy, but the pilot was able to escape the submerged aircraft.
The investigation
The BEA investigation focused on determining the cause of the engine failure and the accuracy of the fuel levels on board. Investigators examined the wreckage, which had been recovered from the bottom of the pond. While the fuel system contained water from submersion, no prior mechanical malfunctions were found in the engine or the fuel circuit.
Data from the aircraft's GNSS unit and the pilot's testimony were used to reconstruct the flight path. The investigation also looked into the refueling procedures used by the operator, noting that refueling was performed via a manual process without a flow meter. The investigation also examined the pilot's method for estimating fuel, which relied on visual inspections of the tanks rather than cockpit gauges.
Findings
- The engine stopped due to fuel exhaustion.
- The pilot's estimate of fuel consumption (approximately 60 l/h) was likely lower than the actual consumption, which can reach up to 80 l/h when the aircraft is at maximum takeoff weight.
- The amount of fuel loaded during the final refueling was likely overestimated. The visual inspection of the fuel level may have been inaccurate because the aircraft was parked on uneven ground, which could have biased the reading by 20 to 30 liters.
- The low-level fuel warning light remained unlit during the flight, which may have been caused by a broken wire connecting the sensor to the cockpit indicator.
- The refueling process lacked a flow meter, making it difficult to precisely track the amount of fuel added to the tanks.