Airworthiness Directive · Amendment 39-10421 · Bell Helicopter Textron, Inc. Model 412 Helicopters and Agusta S.p.A. Model AB412 Helicopters
Bell Helicopter Textron, Inc. Model 412 Helicopters and Agusta S.p.A. Model AB412 Helicopters
Superseded. A later AD replaced this one: AD 2001-09-11. Comply with the one in force.
Bell Helicopter Textron, Inc. Model 412 helicopters, serial numbers (S/N) 33001 through 33213, 34001 through 34024, 36001 through 36121, 46400 through 46434, 46437, and Agusta S.p.A. Model AB412 helicopters, S/N prior to and including S/N 25806, and S/N 25901; certificated in any category.
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.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
