What happened
On March 20, 2011, a Bell 206B helicopter, registration I-ETBR, was performing a tourist flight near Champoluc, Italy. During the takeoff phase, after reaching an altitude of approximately 3 meters, the aircraft began to rotate uncontrollably to the right. Despite the pilot applying full left pedal input, the rotation could not be arrested. To prevent further complications, the pilot attempted an autorotative landing. During the contact with the ground, the main rotor blades struck a nearby slope, causing the helicopter to tip onto its right side. There were no injuries among the four occupants on board.
The investigation
The investigation focused on the wreckage and the mechanical state of the aircraft. Examination of the debris revealed that the main rotor had completely detached from the fuselage due to a dynamic overload failure of the main mast. The main rotor blades sustained damage across approximately two-thirds of their length. Additionally, the tail rotor assembly was separated from the fuselage because the tail boom fractured near the vertical stabilizer, also showing signs of dynamic overload. The investigation determined that the damage to both the main and tail rotors was consistent with an impact with the ground while the engine was delivering high power.
Findings
- The primary cause of the accident was a loss of control during takeoff while operating at maximum takeoff weight from an altitude of 1,500 meters.
- The investigation identified a likely occurrence of Loss of Tail Rotor Effectiveness (LTE).
- As the aircraft climbed, a reduction in lift due to ground effect occurred. The pilot was unable to timely correct the natural tendency of the helicopter to yaw to the right.
- Several contributing factors exacerbated this yawing tendency, including high takeoff weight, low air density, low translational velocity, and high power applied to the rotor.
- A possible, though undocumented, wind component from the left or from behind may have further contributed to the loss of directional control.