Airworthiness Directives; Turbomeca S.A. Turboshaft Engines

We are adopting a new airworthiness directive (AD) for all Turbomeca S.A. Arriel 1A1, 1A2, 1B, 1C, 1C1, 1C2, 1D, 1D1, 1E2, 1K1, 1S, 1S1, 2B, 2B1, 2C, 2C1, 2C2, 2S1, and 2S2 turboshaft engines. This AD requires an initial one-time vibration check of the engine accessory gearbox (AGB) on certain higher risk Arriel 1 and Arriel 2 model engines. This AD also requires repetitive vibration checks of the engine AGB for all Arriel 1 and Arriel 2 engines at every engine shop visit. This AD was prompted by reports of uncommanded in-flight shutdowns on Turbomeca S.A. Arriel 1 and Arriel 2 engines following rupture of the 41-tooth gear forming part of the 41/23-tooth bevel gear located in the engine AGB. We are issuing this AD to prevent failure of the engine AGB, which could lead to in-flight shutdown and damage to the engine, which may result in damage to the aircraft.