Airworthiness Directives; Turbomeca Arriel 1B, 1D, and 1D1 Turboshaft Engines

The FAA is adopting a new airworthiness directive (AD) for Turbomeca Arriel 1B, 1D, and 1D1 turboshaft engines. This AD requires inspecting the 2nd stage nozzle guide vanes (NGV2) for wall thickness. This AD results from one instance of a fractured 2nd stage turbine blade followed by an uncommanded engine shutdown. We are issuing this AD to detect and prevent perforation of the NGV2 that could cause fracture of a turbine blade that could result in an uncommanded engine in-flight shutdown on a single-engine helicopter.