Action
Final rule; request for comments.
Summary
We are superseding an existing airworthiness directive (AD) for General Electric Company (GE) CF6-45 and CF6-50 series turbofan engines with certain low-pressure turbine (LPT) rotor stage 3 disks installed. That AD currently requires initial and repetitive borescope inspections of the high-pressure turbine (HPT) rotor stage 1 and stage 2 blades for wear and damage, including excessive airfoil material loss. That AD also requires fluorescent-penetrant inspection (FPI) of the LPT rotor stage 3 disk under certain conditions and removal of the disk from service before further flight if found cracked. That AD also requires repetitive exhaust gas temperature (EGT) system checks (inspections). This AD requires HPT rotor stage 1 and stage 2 blade inspections and EGT system inspections. This AD also requires FPI of the LPT rotor stage 3 disk under certain conditions, removal of the disk from service before further flight if found cracked, and an ultrasonic inspection (UI) of the LPT rotor stage 3 disk forward spacer arm. This AD also requires initial and repetitive engine core vibration surveys and reporting to the FAA any crack findings, disks that fail the UI, and engines that fail the engine core vibration survey. This AD was prompted by reports received of additional causes of HPT rotor imbalance not addressed in AD 2010-12-10, and two additional LPT rotor stage 3 disk events. We are issuing this AD to prevent critical life-limited rotating engine part failure, which could result in an uncontained engine failure and damage to the airplane.