Airworthiness Directives; Turbomeca S.A. Turboshaft Engines

We propose to adopt a new airworthiness directive (AD) for all Turbomeca S.A. ARRIEL 2C, 2C1, 2C2, 2S1, and 2S2 turboshaft engines with modification TU34 or TU34A installed. This proposed AD was prompted by torque conformation box (TCB) failures. This proposed AD would require inspecting the TCB for correct resistance values and removing TCBs that fail inspection before further flight. We are proposing this AD to prevent failure of the TCB which could lead to loss of engine thrust control and damage to the aircraft.