Airworthiness Directives; Turbomeca S.A. Turboshaft Engines

We are superseding an existing airworthiness directive (AD) for certain Turbomeca S.A. Arriel 2B and 2B1 turboshaft engines. That AD currently requires accomplishment of the TU166 modification. This new AD requires adding the Arriel 2S2 and 2C2 engines to the applicability of engines requiring the TU166 modification with different compliance times. This AD was prompted by reports of an accident involving a twin-engine helicopter powered by two Arriel 2S2 engines. We are issuing this AD to prevent rupture of a gas generator (GG) turbine blade, which could result in an uncommanded in-flight shutdown and a forced landing or accident.