Action
Notice of proposed rulemaking (NPRM).
Summary
We propose to supersede airworthiness directive (AD) 2013-15- 09, which applies to all Pratt & Whitney Division (PW) PW4074, PW4074D, PW4077, PW4077D, PW4084D, PW4090, and PW4090-3 turbofan engine models with certain second-stage high-pressure turbine (HPT) air seals, installed. AD 2013-15-09 currently requires initial and repetitive inspections for cracks in second-stage HPT air seals. Since we issued AD 2013-15-09, we received reports of cracking in the original location on two additional part numbers (P/Ns) as well as reports of through- cracks in a new location in the second-stage HPT air seal. PW has developed a redesigned second-stage HPT air seal that addresses the cracking condition in both locations. This proposed AD would expand the applicability of AD 2013-15-09 to include additional P/Ns, require replacement of the mating hardware if the second-stage HPT air seal is found with a through-crack, and add mandatory terminating action to the repetitive inspections. We are proposing this AD to prevent failure of the second-stage HPT air seal, which could lead to uncontained engine failure and damage to the airplane.