Airworthiness Directives; Bell Helicopter Textron Canada Limited

We are adopting a new airworthiness directive (AD) for certain Bell Helicopter Textron Canada Limited (Bell) Model 206L-1, 206L-3, and 206L-4 helicopters. This AD requires installing a placard and revising the limitations section of the rotorcraft flight manual (RFM). This AD was prompted by several incidents of third stage engine turbine wheel failures caused by excessive vibrations at certain engine speeds during steady-state operations. The actions of this AD are intended to prevent turbine failure, engine power loss, and subsequent loss of control of the helicopter.