What happened
On October 9, 2009, a Eurocopter AS 350 B2, registration LN-ODU, was performing a commercial passenger flight near Store Hoggarvatnet in Rogaland, Norway. The aircraft was transporting four workers to a dam construction site. During the final approach to a landing site on a relatively flat hilltop, the helicopter was flying at approximately 60 knots before slowing to 10-15 knots at a very low altitude.
As the pilot attempted to manage the descent, the aircraft suddenly began a rapid rotation to the left. Despite the pilot'-s efforts to apply right pedal and adjust the collective, the rotation intensified. The centrifugal forces became so great that the pilot was unable to reach the engine controls to shut down the engine. The helicopter completed several rotations before impacting the ground in a dry riverbed. While the aircraft sustained significant damage to the fuselage, tail boom, and main rotor blades, the crew and passengers managed to evacuate. Only one person sustained minor injuries.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the wreckage and analyzed video footage recorded by a passenger, which showed the aircraft spinning uncontrollably for approximately 14 seconds before impact. Technical inspections of the aircraft focused on the tail rotor assembly.
Metallurgical analysis conducted by the Norwegian Defence Research Establishment (FFI) revealed a fatigue crack in the blade horn, a component responsible for regulating the pitch of the tail rotor blades. The investigation determined that the crack originated from a surface irregularity, likely introduced during the manufacturing process, which had been developing over time.