Airworthiness Directives; Turbomeca S.A. Arriel Models 1A, 1A1, 1B, 1D, and 1D1 Turboshaft Engines

This amendment adopts a new airworthiness directive (AD) that is applicable to Turbomeca S.A. Arriel models 1A, 1A1, 1B, 1D, and 1D1 turboshaft engines. This action requires installation of containment shield rings around the free turbine blade area, and installation of a double support around the gearbox free turbine bearing housing. This amendment is prompted by two reports of the cantilevered axis of the free turbine moving from its design position and inducing blade trajectories outside the current design free turbine containment area. This condition can lead to uncontainment of the free turbine during an overspeed event. The actions specified in this AD are intended to prevent uncontainment of the free turbine during an overspeed event, resulting in damage to the helicopter.