What happened
On 27 October 2018, an Agusta AW169 helicopter, registration G-VSKP, crashed at the King Power Stadium in Leicester during a private flight. The accident resulted in 5 fatalities, including the pilot and four passengers. The impact destroyed the aircraft.
The investigation
Technical examinations of the wreckage focused on the helicopter's yaw control system. Investigators discovered that the input lever mechanism had become disconnected from the control shaft. Key components, including the pin, spacers, and a locating bearing, were missing from the lever. Furthermore, the locking nut and pin carrier were found to be fused together, and the split pin had been sheared off.
Detailed analysis using Computed Tomography (CT) scanning revealed that the nut and pin carrier had undergone friction welding. The scan of the duplex bearing showed significant damage to the inner bearing races, cage fractures, and the presence of metallic and black dust debris within the raceways. Evidence suggested that the control shaft had been rotating, which caused the shaft to effectively unscrew from the nut, severing the connection to the actuator lever mechanism.
Findings
- The loss of aircraft control was caused by the disconnection of the tail rotor actuator control shaft from the actuator lever mechanism.
- This disconnection disabled the feedback mechanism, rendering the yaw stops ineffective.
- Without the feedback mechanism, the tail rotor actuator moved the blade pitch to its physical limit, resulting in an uncontrollable right yaw.
- High torque and force applied to the castellated nut caused it to friction weld to the pin carrier and shear the split pin.
- Damage to the duplex bearing and increased torque loads on the nut were consistent with the rotation of the control shaft.