The FAA is proposing to adopt a new airworthiness directive (AD) for the Sikorsky Model S-70, S-70A, S-70C, S-70C (M), and S-70C (M1) helicopters with General Electric (GE) T700-GE-401C or T700-GE-701C engines installed. This proposed AD is prompted by a reevaluation of the method for determining the life limit for certain GE engine gas generator turbine (GGT) rotor parts and the determination that these life limits need to be based on low cycle fatigue events instead of hours time-in-service.

The proposed actions are intended to establish new fatigue life limits for certain GGT rotor parts to prevent fatigue failure of a GGT rotor part, engine failure, and subsequent loss of control of the helicopter.

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