AAIB Report: Eurocopter EC135T1, corrosion-initiated fracture of a main rotor actuator tie bar
Eurocopter EC135T1 (VP-CPS), corrosion-initiated fracture of a main rotor actuator tie bar, Owen Roberts International Airport, Cayman Islands.
At the start of a ‘training and search’ detail in the Cayman Islands, the pilot lifted the helicopter to a height of approximately four feet and felt the cyclic control stick shake and exert a rearwards force. He immediately lowered the collective lever and the helicopter landed heavily, sustaining damage to the tail boom, landing gear and transmission deck.
A subsequent inspection of the helicopter revealed the longitudinal axis of the main rotor actuator had failed. A tie bar within the actuator had suffered pitting corrosion, leading to intercrystalline corrosion and cracking which resulted in overload failure of the remaining material. It is possible that moisture penetrated into the actuator and allowed the tie bar to corrode. The environment conditions of the Cayman Islands may have contributed to the corrosion.
Safety actions have been taken to ensure the continued airworthiness of the worldwide fleet and to review the design of the actuator to prevent moisture ingress.