Summary
We propose to adopt a new airworthiness directive (AD) for all Turbomeca S.A. Arriel 1A1, 1A2, 1B, 1C, 1C1, 1C2, 1D, 1D1, 1E2, 1K1, 1S, and 1S1 turboshaft engines. This proposed AD was prompted by several reports of uncommanded in-flight shutdown (IFSD) on Arriel 1 engines. This proposed AD would require performing a high gas generator speed (NG) rating vibration check. We are proposing this AD to prevent an uncommanded in-flight shut-down of the engine, which could result in an emergency landing.