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Federal Register / Vol. 86, No. 142 / Wednesday, July 28, 2021 / Rules and Regulations Manual does not provide dimensions that bound the areas making HPT disk replacement subjective.
The FAA agrees that it is difficult to differentiate between a surface crack and through-crack; therefore, the FAA
removed references to through-crack from this AD. The FAA notes that any crack, in any direction, found in the HPT 2nd-stage air seal assembly, requires removal of the HPT 2nd-stage air seal assembly from service. As stated in an earlier response, the FAA added Figure 1 to show the locations of the HPT 2nd-stage air seal assembly that require inspection for cracks. However, the FAA is not providing dimensions that bind the areas. If the inspections of the HPT 2nd-stage air seal assembly reveal a crack in the shaded regions of Figure 1, which extends towards the knife-edge region, the HPT 2nd-stage air seal assembly must be removed from service.
Request To Clarify Engine Shop Visit Delta requested that the FAA clarify the definition of engine shop visit related to which engine flanges the FAA
considers major mating engine flanges. Delta requested that the FAA
exclude the low-pressure compressor LPC module flange as a major mating engine flange because LPC module life limited parts LLPs can be swapped while the engine is installed on the aircraft. Delta reasoned that the separation of the LPC module flange should not require replacement of the HPT 2nd-stage air seal assembly. These LPC swaps may extend time between engine shop visits if the LLPs are located in the LPC.
The FAA determined the need to revise the definition of engine shop visit by replacing separation of major mating engine flanges with separation of the N or M engine flange. If the LPC swap does not involve separating the N or M engine flange, then the compliance time for replacing the HPT
2nd-stage air seal assembly has not occurred as required by this AD.

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Request To Update the Definition of Piece-Part Opportunity Delta requested that the FAA update the definition of piece-part opportunity from when the part is completely disassembled to any time the seal is removed from the HPT
module. Delta reasoned that while the HPT 2nd-stage air seal assembly is referred to as an assembly, the HPT

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2nd-stage air seal assembly cannot be dissembled.
The FAA partially agrees and updated the definition to clarify what constitutes piece-part opportunity for the HPT
1st-stage disk, HPT 2nd-stage hub, and HPT 2nd-stage air seal assembly.
Request To Update the Definition of Part Eligible for Installation Delta requested that the FAA update the definition of part eligible for installation to remove paragraph i3ii and to refer only to An HPT
2nd-stage air seal assembly that is not P/
N 1A8209 or 1A8209001. Delta reasoned that paragraph i3ii of the NPRM, which states that an HPT 2ndstage air seal assembly that has been modified using the service information is eligible for installation, is unnecessary because the HPT 2nd-stage air seal assembly receives a new P/N, which is not P/N 1A8209 or 1A8209
001, after repair.
The FAA agrees and revised the definition of an HPT 2nd-stage air seal assembly that is eligible for installation, now in paragraph h3 of this AD, to refer to an HPT 2nd-stage air seal assembly with a P/N other than 1A8209
or 1A8209001.
Request To Update Service Information Revision MTU requested that the FAA
reference PW SB PW2000 72754, Revision No. 3, dated August 14, 2019, in this AD instead of Revision No. 2, dated April 30, 2019.
The FAA agrees. The FAA updated PW SB PW2000 72754 to Revision No.
3, dated August 14, 2019, throughout this AD.
Request To Update the Service Information Description MTU requested that the FAA update the service information description in the Other Related Service Information paragraph of the NPRM Related Service Information of this AD to include the replacement and modification of the HPT 2nd-stage air seal assembly.
The FAA agrees. The FAA updated the service information description in the Related Service Information paragraph in this AD.
Request To Update the Costs of Compliance UAL requested that the Costs of Compliance include additional costs such as delays in engine builds and modifications. UAL reasoned that piece-

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part modification of the HPT 2nd-stage air seal assembly, mating HPT 1st-stage disk, and HPT 2nd-stage hub are independent of each other. Scraping all parts proposed by paragraph g2iii of the NPRM paragraph g1iii of this AD will force engine centers to delay routing the mating HPT 1st-stage disk and HPT 2nd-stage hub for modification until the HPT 2nd-stage air seal assembly is inspected, thus delaying an engine build or incurring costs while the mating HPT 1st-stage disk and HPT
2nd-stage hub are partially or fully scrapped.
The FAA disagrees with updating the costs of compliance. The cost analysis in AD rulemaking actions typically includes only the costs associated with complying with the AD and does not include secondary costs. The FAAs cost estimate includes the work hours and parts costs to perform the required actions.
No Comments on This AD
ALPA supported the AD and appreciated the opportunity to comment. Boeing had no comments.
Conclusion The FAA reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed.
Accordingly, the FAA is issuing this AD
to address the unsafe condition on these products. Except for minor editorial changes, and any other changes described previously, this AD is adopted as proposed in the NPRM.
None of the changes will increase the economic burden on any operator.
Related Service Information The FAA reviewed PW SB PW2000
72754, Revision No. 3, dated August 14, 2019, and PW SB PWF117 72402, Revision No. 2, dated May 3, 2019. The SBs describe procedures for replacing or modifying the HPT 2nd-stage air seal assembly.
Interim Action The FAA considers this AD to be an interim action. The FAA may consider additional rulemaking based on further investigation of the unsafe condition.
Costs of Compliance The FAA estimates that this AD
affects 445 engines installed on airplanes of U.S. registry.
The FAA estimates the following costs to comply with this AD:

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