What happened
On June 7, 2016, a Bell 47 G2 helicopter, registration F-GANX, was performing agricultural work near Grateloup-Saint-Gayrand, France. The mission involved "whitening" greenhouses by spraying a white liquid to regulate light and temperature.
While performing the final rotation of the day, the pilot noticed an area of the greenhouses that had been insufficiently treated. To correct this, the pilot deviated from his planned flight path to treat the missed section before attempting to return to his original trajectory by passing under a medium-voltage power line. During this maneuver, the main rotor struck the electrical lines, causing the rotor mast to be torn from the aircraft. The helicopter became uncontrollable and crashed into the greenhouses, resulting in the destruction of the aircraft and one injury to the pilot.
The investigation
The investigation focused on the aircraft's condition, the flight path, and the pilot's circumstances. Examination of the wreckage confirmed that the Bell 47 G2 was fully functional prior to the collision. The impact with the electrical wires caused the rotor mast and main rotor to be ripped away.
The investigation also reviewed the pilot's experience and the environmental constraints. The pilot was highly experienced, with approximately 9,500 total flight hours, including 5,000 hours on this specific type. While the pilot was familiar with the area and the location of the power lines, the investigation noted that the vertical clearance between the lowest point of the lines and the greenhouse roofs was extremely limited, especially considering the height of the rotor blades during flight.
Findings
Investigators determined that the accident was caused by the pilot's decision to deviate from the planned trajectory, which led to an improvised and less secure flight path.
Several contributing factors were identified:
- The narrow margin of clearance between the power lines and the greenhouse structures relative to the aircraft's rotor height.
- The pilot's physical and psychological fatigue.
- Time pressure and a lapse in concentration associated with performing the final mission rotation of the day.