What happened
On October 12, 2011, an AS350 B3 helicopter, registration F-GJPH, was performing a utility flight to deliver and collect electronic equipment at a television relay station located on the Pibeste peak. The flight was operated by SAF. Before landing, the pilot had contacted ground technicians to ensure the landing area was clear of unsecured objects and had provided safety instructions.
During the landing approach, the pilot and flight assistant failed to notice a folded tarp located in an open electronic bay at the edge of the landing platform. As the helicopter entered the flare, the rotor downwash lifted the tarp, causing it to deploy vertically. To avoid a direct strike with the rotor blades, the pilot applied firm collective pitch to force the aircraft onto the ground. This maneuver, combined with the interference from the tarp, caused the aircraft to enter ground resonance. The helicopter drifted toward the edge of the platform, with the tail boom overhanging the precipice. Despite intense vibrations and the pilot's attempts to adjust rotor speed, the aircraft remained unstable until the pilot successfully engaged the rotor brake and engine shutdown switches, bringing the aircraft to a halt.
The investigation
The investigation focused on the mechanical failure of the rotor system and the sequence of events leading to the loss of control. Investigators examined the main rotor and identified a broken arm on the starflex component. Physical inspection of the aircraft revealed extensive damage, including broken or deformed fuselage longerons, a twisted tail boom, and a ruptured upper right cabin section. Most of this structural damage was attributed to the forces generated during the ground resonance.
Analysis of the flight parameters showed a drop of approximately 50 rpm lasting for two seconds. This transient loss of rotor speed was linked to the drag induced by the tarp, which also caused the starflex arm to fail. The investigation also reviewed the crew's preparations and the ground personnel's actions.