AD FAA-2011-0861

This amendment adopts a new airworthiness directive (AD) for the specified Agusta S.p.A. (Agusta) helicopters with a certain tail rotor special hub plug (hub plug) installed. This action requires a one-time inspection to determine the tightening torque value of the hub plug, and depending on the inspection results, replacing certain parts or disassembling the tail rotor hub and blades assembly and inspecting for damage. If the tightening torque value is between 600 kgcm and 700 kgcm, the lock washer and o-ring must be replaced with airworthy parts, and no further action is required. If the tightening torque value is greater than 700 kgcm, the hub plug must be replaced with an airworthy part. Torque the new hub plug to the specified tightening torque between 600 and 700 kgcm. If the tightening torque value of the hub plug is less than 600 kgcm, the tail rotor hub and blades assembly must be disassembled and inspected for damage. If a part is found that is outside allowable damage tolerances, that part must be replaced with an airworthy part. This amendment is prompted by the discovery that a wrong tightening torque value for the hub plug was contained in a revision to the helicopter maintenance manual. The actions specified in this AD are intended to detect an improperly torqued hub plug that could lead to tail rotor failure and subsequent loss of control of the helicopter.