Accident
On 20 March 2011, at approximately 11:00 UTC, a Bell 206B helicopter, registration I-ETBR, was conducting a tourism flight from Champoluc, Aosta, Italy. The aircraft, carrying a pilot and three passengers, was destroyed in the accident. No injuries were reported among the occupants. The weather was described as good with sunny conditions and good visibility; the ground was covered with approximately 0.5 meters of snow.
According to the pilot, the accident occurred during takeoff. After reaching a height of about 3 meters above ground, the helicopter began to rotate to the right despite full left pedal input. Unable to stop the rotation, the pilot decided to return to the ground in autorotation. Upon touchdown, the main rotor blades struck a nearby slope, and the helicopter rolled onto its right side.
Investigation
Examination of the wreckage revealed that the main rotor had completely separated from the fuselage due to a fracture of the main transmission shaft. The fracture surface exhibited dynamic overload characteristics. The entire rotor assembly, with blades damaged along approximately two-thirds of their length, was found near the rear of the wreckage. The tail rotor had also separated from the fuselage due to a fracture of the tail boom near the fin. Both tail rotor blades were severed near the root, while the 90-degree gearbox remained intact. The lower fin was damaged along about half its length. All fractures showed dynamic overload characteristics. This damage pattern indicated that the main and tail rotor blades struck the ground while the engine was delivering high power.
Causes
The official investigation attributed the cause of the accident to a loss of control during takeoff while operating at full load from an altitude of 1500 meters. It was considered reasonably probable that after lift-off, during the reduction of ground effect, the pilot did not timely correct the helicopter's natural tendency to yaw to the right. This tendency, accentuated by the combined effects of maximum takeoff weight, low air density, low translational speed, high rotor power, and a possible (though undocumented) left or tail wind component, degenerated to the point where the tail rotor became completely ineffective, rendering the helicopter uncontrollable. This phenomenon is known as Loss of Tail Rotor Effectiveness (LTE).