What happened
On October 16, 2007, an Aerospatiale SA 315B “Lama”, registration I-AVIF, was performing external load operations in the Val di Rabbi region. The mission involved transporting materials for the construction of avalanche barriers from a loading base at Malga Brodolona to a base at Castel Pagano.
After completing its thirteenth delivery of cement pallets, the helicopter was returning to the loading site with only the necessary sling attachments on the hook. While traversing a mountain pass (saddle) at an elevation of approximately 2,400 meters, the aircraft lost control. An observer at the loading base witnessed the helicopter begin to rotate rapidly around its vertical axis before plunging into a steep, rocky slope at an altitude of roughly 2,300 meters. The aircraft was destroyed upon impact, though the pilot sustained only minor injuries.
The investigation
The ANSV investigation focused on the wreckage distribution and the mechanical state of the aircraft. Investigators recovered fragments of the tail rotor blades and the tail boom, which had separated from the main fuselage. Notably, the investigation found that the tail rotor assembly had been struck by the external load cable.
Physical evidence showed that the 9.84-meter load cable had struck the rocky terrain at the mountain pass. This impact triggered a pendulum effect, causing the cable to whip upward and entangle with the tail rotor. The resulting force was so great that it caused the tail rotor transmission shaft to fracture at the 9-degree gearbox, leading to the complete detachment of the tail rotor assembly. The investigation also noted that the main rotor blades struck the rear section of the tail boom during the subsequent uncontrolled descent.
Findings
- The primary cause of the accident was the entanglement of the external load cable with the tail rotor, which led to the loss of anti-torque control and the subsequent detachment of the tail rotor assembly.
- The entanglement was initiated when the hook and the end of the cable struck the terrain while the pilot was crossing the mountain saddle.
- The pilot failed to maintain an adequate safety altitude relative to the terrain and environmental obstacles during the flight over the orographic feature.
- While microclimatic conditions (such as localized turbulence or downdrafts) at the saddle could have contributed to a sudden loss of altitude, the pilot's failure to account for the terrain's topography was a decisive factor.