Summary
We propose to adopt a new airworthiness directive (AD) for certain 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 a finding that the engine's tachometer unit cycle counting feature is unreliable. This proposed AD would require daily post-flight checks of the engine tachometer's unit cycle counting feature. This proposed AD would also require ground-run functional checks within every 1,000 operating hours. This proposed AD was prompted by detailed analysis and review of the accuracy of the engine's tachometer cycle counting feature. We are proposing this AD to prevent uncontained engine failure and damage to the helicopter.