Airworthiness Directives; Turbomeca S.A. Turboshaft Engines

We are superseding an existing airworthiness directive (AD) for all Turbomeca S.A. Arriel 1A, 1A1, 1A2, 1B, 1C, 1C1, 1C2, 1D, 1D1, 1E, 1E2, 1K, 1K1, 1S, and 1S1 turboshaft engines. That AD currently requires initial and repetitive visual inspections for erosion caused by dust ingestion and, if necessary, cleaning of the gas generator (module M03). This new AD requires determining the engine history; performing a one-time visual inspection of the axial compressor for erosion; performing initial and repetitive cleaning of the gas generator hollow shaft; and replacing the rear bearing if the amount of dust collected during cleaning exceeds 8 grams. This AD also includes an optional terminating action. This AD was prompted by in-service experience which has shown that dust inside the gas generator hollow shaft may be found when the axial compressor wheel has less erosion than initially assessed. We are issuing this AD to prevent an unbalance of the gas generator rotating assembly, which may lead to gas generator rear bearing failure, and uncommanded engine shutdown.