History of the Flight
The pilot departed for a spraying mission over polytunnels. After a 15-minute first rotation, the pilot landed and the task specialist added approximately 20 liters of fuel and whitening product while the rotor was turning. During the subsequent flight, after about 20 minutes, the engine stopped while the helicopter was over a polytunnel. The pilot continued straight ahead toward a ploughed field and performed a sliding landing. The soft ground caused the skids to sink. The pilot applied cyclic input to prevent a rollover, and the helicopter bounced several times before stopping.
Meteorological Information
Météo-France reported wind from 10° to 50° at 4 to 6 knots, gusting to 11–13 knots, visibility greater than 10 km, clear sky, temperature 20°C, dew point 8°C, and QNH 1021 hPa.
Pilot Information
The 56-year-old pilot held a CPL(H) license with a Bell 47 rating and had 638 total flight hours, with 35 hours in the previous three months on the accident type. He had completed training on whitening polytunnels at the operator.
Statements
The pilot stated that fuel quantity was visually checked using a diagram on the bubble sight. The two fuel tanks are interconnected; refueling can be done from one side. After the first flight, he estimated 40 liters remained and asked the task specialist to add 20 liters. The task specialist confirmed visually seeing about 40 liters and activated the pump nozzle for approximately 30 seconds, estimating 20 liters added. After balancing, the level appeared to indicate 60 liters total. The task specialist indicated no leaks were observed. The pilot noted that the low fuel level light was unreliable and lit prematurely.
Helicopter Information and Fuel System
F-GANY, a Bell 47G-2 built in 1956 with a Lycoming VO-435-A1 engine, was purchased by the operator in 2003. The fuel system includes interconnected tanks, a gauge, and bleed valves. The operator's refueling procedure involves visual level checks using a diagram on the bubble sight. Refueling with rotor turning was authorized per the company's manual.
Examination of Helicopter and Bleed Valves
During a re-enactment of the refueling, a large leak was observed at the left-hand fuel tank bleed valve even when closed. The valve was removed for examination. Flow tests showed the right-hand valve had a flow rate of about 4 L/min when fully open, while the left-hand valve had 1–2 L/min. With 60 liters at takeoff, 20 minutes of flight consumed about 23 liters, implying a 37-liter loss consistent with a leak of 1–2 L/min. Disassembly of the left-hand bleed valve revealed debris that prevented complete closure, allowing fuel to leak. The right-hand valve was clean and functioned normally.