Summary
We are revising an earlier proposed 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, which proposed establishing new fatigue life limits for certain GE engine gas generator turbine (GGT) rotor parts. The proposed AD was 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 (LCF) events instead of hours time-in- service. This action would retain the previously proposed requirements but correct the life limit formula for a certain GGT rotor part. The proposed actions are intended to prevent fatigue failure of a GGT rotor part, engine failure, and subsequent loss of control of the helicopter.