What happened
On August 5, 2005, a Robinson R4SO helicopter was performing a local flight in the mountains of France. The flight began at the Grenoble-Le-Versoud aerodrome, carrying a pilot and one passenger. After landing at a restaurant helipad near Chatillon in Diois, the crew attempted to return to Grenoble.
While navigating the valley leading to the Col de la Menée, the aircraft was observed flying at a high speed and low altitude. As the helicopter approached a ravine, the pilot attempted to gain altitude and executed a rapid right-hand turn. During this maneuver, the rear section of the aircraft struck the tops of trees, causing the tail boom to separate from the fuselage. The cabin subsequently struck the ground approximately 200 meters below the impact site, where a post-crash fire erupted.
The investigation
Investigators recovered the horizontal stabilizer and the tail rotor from the treetops, noting significant deformation on the leading edge of the stabilizer. Examination of the wreckage confirmed that the engine was delivering power and the drive shaft was rotating at the moment of the initial impact. While the engine, main transmission, and cabin were destroyed by the fire, the rear transmission and rear drive shaft were not recovered.
Findings
- The investigation established that the pilot's decision to fly at low altitude in close proximity to the terrain was the primary cause of the accident.
- The aircraft was maneuvering near trees and terrain during a high-speed turn.
- A tailwind gust may have caused the aircraft to lose several feet of altitude during the maneuver.
- It is also possible that a reflexive control input on the collective pitch was made in an attempt to increase the aircraft's pitch, contributing to the loss of altitude.