Action
Notice of proposed rulemaking (NPRM).
Summary
The FAA proposes to supersede Airworthiness Directive (AD) 2012-02-07, which applies to certain General Electric Company (GE) CF6- 45 and CF6-50 series model turbofan engines with a specified low- pressure turbine (LPT) rotor stage 3 disk installed. AD 2012-02-07 requires inspections of high-pressure turbine (HPT) and LPT rotors, engine checks, vibration surveys, an optional LPT rotor stage 3 disk removal after a failed HPT blade borescope inspection (BSI) or a failed engine core vibration survey, establishes a lower life limit for the affected LPT rotor stage 3 disks, and requires removing these disks from service at times determined by a drawdown plan. Since the FAA issued AD 2012-02-07, four additional events of separation of the LPT rotor assembly have been reported resulting in the LPT rotor assembly departing the rear of the engine. The manufacturer has improved the design of the LPT rotor stage 3 disk. This proposed AD would continue to require inspections of HPT and LPT rotor stage 1 and stage 2 blades, vibration surveys, and use of a lower life limit for the affected LPT rotor stage 3 disks. As a terminating action to the inspections, engine checks, and vibration surveys, this proposed AD would require removal and replacement of the LPT rotor stage 3 disk with a redesigned LPT rotor stage 3 disk. This proposed AD would also revise the compliance time of the drawdown plan for the removal and replacement of the LPT rotor stage 3 disk. This proposed AD would also prohibit the installation or reinstallation of certain LPT rotor stage 3 disks. The FAA is proposing this AD to address the unsafe condition on these products.