Airworthiness Directives; Bell Helicopter Textron, Inc. Model 412 Helicopters and Agusta S.p.A. Model AB412 Helicopters

This amendment adopts a new airworthiness directive (AD) that is applicable to Bell Helicopter Textron, Inc. (Bell) Model 412 helicopters and Agusta S.p.A. (Agusta) Model AB412 helicopters. This action requires a temporary reduction of the never-exceed velocity (Vne) limitation until an inspection of the tail rotor yoke (yoke) assembly for fatigue damage and installation of a redesigned yoke flapping stop are accomplished. Recurring periodic and special inspections to detect occurrences of yoke overload are also required. This amendment is prompted by laboratory tests and engineering analyses that indicated that the yoke assembly is susceptible to fatigue damage due to unforeseen static and dynamic loading of the tail rotor against the original flapping stop. The actions specified in this AD are intended to prevent fatigue failure of the yoke that could result in loss of control of the tail rotor and subsequent loss of control of the helicopter.