Helicopter accident at Pic de Pibeste due to starflex failure

Incident Overview and Context On October 12, 2011, at 16:25 local time, an AS350 B3 helicopter registered F-GJPH, operated by Société SAF, was involved in an accident at the Pic de Pibete platform in the Hautes-Pyrénées (65). The platform, located at an altitude of 3,950 feet, had an area of approximately 40 square meters. The helicopter sustained severe damage as a result of the incident. The flight was intended to deliver equipment to technicians working at the television relay station and to retrieve two electronic bays. Prior to takeoff from the Ger base, the pilot contacted the technicians to ensure no unsecured objects were near the platform and provided safety instructions for the landing. During the approach, the pilot and his flight assistant conducted a visual check for potential hazards but failed to detect a tarp that was likely folded inside one of the electronic bays at the edge of the landing zone. ## Sequence of Events and Damage During the final approach, turbulence generated by the main rotor in ground effect lifted the tarp, which deployed vertically. The pilot spotted it through the rear left window and anticipated contact with the rotor blades. He firmly pushed the helicopter to the ground using the collective pitch control and countered violent reactions on the cyclic control. The helicopter entered ground resonance while moving backward and to the right toward the cliff. The pilot's attempts to vary the rotor speed using the throttle lever to reduce vibration were ineffective. He instructed his assistant to evacuate the helicopter. Despite the high-amplitude oscillations of the airframe, the pilot managed to activate the engine start/stop switch and the rotor brake on the upper panel. The resonance stopped, and the helicopter came to a rest with its skids flat on the platform and the rear beam over the void. Visual inspection of the main rotor revealed a broken branch of the starflex. This damage explained the control difficulties and the entry into ground resonance upon contact with the ground. Two of the three rotor blades showed transfer marks from the tarp material, primarily on their upper surfaces and leading edges. Nearly all the rivets connecting the rear beam to the airframe were missing. The airframe longerons were broken or deformed downward. The cabin was broken on its upper right side and deformed on the left. The rear beam was twisted. Except for the starflex, all these damages were a consequence of the ground resonance. The onboard parameter recorder showed a loss of approximately 50 rpm for two seconds. The drag induced by the tarp was likely the cause of this speed loss and the starflex failure. The pilot had 8,475 total flight hours, including 5,389 on type and 281 in the last three months. He was familiar with the platform and experienced in aerial work. The day before the flight, the pilot had briefed the personnel working on the platform about securing objects in the landing zone. ## Conclusions and Contributing Factors The accident resulted from the starflex failure following the interference of a tarp with the main rotor during landing on the platform. The resulting imbalance caused an uncontrollable ground resonance. Neither the pilot nor his assistant had detected the presence of the folded tarp stored in an open electronic bay. The technicians present on the platform did not have specific training in helicopter-assisted work. They were only aware of the risks through a briefing and did not consider the tarp a danger to the helicopter flight.