Accident Overview
On 26 April 2020, at approximately 11:50 local time, a Bell 47 G2 helicopter registered F-GBOO was destroyed following a loss of yaw control during a mosquito control spraying flight near Sète (Hérault), France. The sole occupant, the pilot, was injured and escaped before the helicopter caught fire. The operator was Giragri 17, and the flight was part of a public interest mission to control mosquitoes.
Flight History
The pilot began operations at 07:15, conducting several spraying rotations in the Vendres and Listel sectors. Each rotation involved landing on a prepared helipad for refueling and refilling larvicide tanks. At 11:49, the pilot took off to reach the next plot, about five kilometers northeast. In straight flight at approximately 20 m height, the pilot heard a noise from the rear and the helicopter began yawing right. Full left pedal input did not regain control. The pilot alternately applied left and right pedals, noting variation in yaw rate but inability to stop the rotation. The helicopter rotated multiple times (estimated at least ten) before crashing on its left side into a field of reeds. The low height prevented a successful autorotation. After the crash, the pilot exited the airframe before the right fuel tank ignited, with fire spreading to the engine and main gearbox (MGB).
Aircraft Information
The Bell 47G-2 is a light helicopter with a counter-clockwise rotating two-blade main rotor and a Lycoming VO-435-A1 piston engine. F-GBOO was equipped with "Simplex" spraying equipment for mosquito control, including two larvicide tanks (total 208 L) and two spray booms. Maximum takeoff weight is 1,111 kg; empty weight was 777 kg including 78 kg for Simplex. At the time of the accident, larvicide tanks were full and fuel tanks contained approximately 70 L, bringing the weight close to maximum.
Wreckage Examination
The wreckage was found in a field with rushes about 1.5 m high. Damage was consistent with low energy impact and steep left bank angle. Blade ground contact led to MGB attachment failure. Elevator, rudder, and collective pitch controls were continuous; cyclic pitch continuity could not be checked. Rudder control functionality was verified. Main rotor drive belts broke due to overload. The tail rotor drive line separated from the MGB on impact and failed suddenly due to overload; it was likely continuous before impact. The tail rotor had little damage. The engine was substantially damaged by fire; throttle control was jammed near idle. Free wheel and clutch had no damage. No mechanical failures were observed that could explain the loss of yaw control.
Pilot Information
The 58-year-old pilot held a valid Commercial Pilot Licence (Helicopters) with 3,175 total flight hours, of which 3,100 were in Bell 47 aircraft, mostly in agricultural work. He had flown approximately 26 hours in the previous 90 days. He reported no fatigue or pressure to take risks, and was not performing any maneuvers when control was lost.
Meteorological Conditions
Estimated conditions at the accident site: wind from 180° at 6 to 11 kt, visibility >20 km, temperature 19 °C, dew point 14 °C, QNH 1,010 hPa, broken cumulus clouds, sea breeze, light to moderate turbulence.
Investigation Conclusions
The investigation did not identify any mechanical failure that could explain the loss of yaw control. The helicopter was flying northeast with a right-hand tailwind of about 10 kt in light to moderate turbulence, heavy and close to maximum weight, and moving slowly. These conditions are conducive to an unanticipated yaw (loss of tail rotor effectiveness, or LTE). While a technical failure cannot be completely ruled out, the scenario of loss of yaw control due to unanticipated yaw is also possible.