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Federal Register / Vol. 86, No. 142 / Wednesday, July 28, 2021 / Rules and Regulations Comment on Operational and Economic Costs FedEx commented that the proposed rule would impact approximately half of its fleet of PW2000 model turbofan engines. The inspection program itself will have a minor operational impact as it can be incorporated into an existing hot section inspection program, but unplanned engine changes will result in local operational impact. FedEx noted that the cost of the on-wing inspection program BSI would be minimal but the cost of engines that need to be removed immediately will have a fairly significant impact. FedEx noted that these operational and economic impacts are acceptable when weighed against the impact of an in-service event.
FAA Response to Comments To Revise the BSI Inspection The FAA determined the need to remove the proposed BSI requirement from this AD based on comments regarding accessibility of inspector training. The FAA may consider additional rulemaking and will consider these comments in the development of any additional requirements.

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Request That Individual Part Serviceability Not Depend on the Inspection Results of Other Parts Delta commented that individual part serviceability should not depend on the inspection results of other parts. Delta also commented that if inspections are not possible which would allow the mating HPT 1st-stage disk or the HPT
2nd-stage hub to be deemed serviceable, independent from inspection status of the HPT 2nd-stage air seal assembly, then the manufacturer should revise the engine manuals to clarify that the mating HPT 1st-stage disk or HPT 2ndstage hub cannot be made serviceable unless an inspection of the HPT 2ndstage air seal assembly indicates it is free of cracks. Delta stated that this would remove the possibility that the mating HPT 1st-stage disk or HPT 2ndstage hub would be made serviceable and then installed in an engine before the HPT 2nd-stage air seal assembly is inspected.
The FAA did not revise this AD in response to this comment. A crack, as identified in the shaded regions of Figure 1 to paragraph g1iii of this AD Figure 1, which extends towards the knife-edge region of the HPT 2ndstage air seal assembly, impacts the serviceability of the mating HPT 1ststage disk and the HPT 2nd-stage hub.
A crack identified in the shaded region of Figure 1 of this AD of the HPT 2ndstage air seal assembly results in the
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requirement to remove the HPT 2ndstage air seal assembly, mating HPT 1ststage disk, and HPT 2nd-stage hub.
Request To Remove Inspections for Parts Being Scrapped Delta requested that the FAA update paragraph g2i of the NPRM
paragraph g1i of this AD to remove the visual inspection, knife-edge coating strip, and FPI of the HPT 2ndstage air seal assembly if the HPT 2ndstage air seal assembly, mating HPT 1ststage disk, and HPT 2nd-stage hub are being scrapped. Further, Delta requested if the HPT 2nd-stage air seal assembly is planned to be scrapped, then the mating HPT 1st-stage disk and HPT 2ndstage hub be allowed to be made serviceable without FPI of the HPT 2ndstage air seal assembly.
The FAA disagrees with the need to change the AD based on this comment.
If the HPT 2nd-stage air seal assembly, HPT 1st-stage disk, and HPT 2nd-stage hub are removed from service, then the inspections required by paragraph g1i of this AD are not applicable.
The inspections are required only if the operator returns the parts to service.
FPI is the only way to ensure the HPT
2nd-stage air seal assembly is free from cracks because an FPI will reveal cracks not detected by a visual inspection. The serviceability of the both the HPT 1ststage disk and HPT 2nd-stage hub is directly dependent on the HPT 2ndstage air seal assembly. If an operator does not FPI the HPT 2nd-stage air seal assembly, then neither the HPT 1st-stage disk nor HPT 2nd-stage disk can be returned to service. The FAA did not change this AD.
Request To Reference Engine Manual for Inspection Instructions FedEx requested that the FAA update paragraph g2i of the NPRM
paragraph g1i of this AD to reference Chapter 725260, Inspection/
Check-01, of the PW2000 Series Engine Manual for instructions to perform the visual inspection, knife-edge coating removal, and FPI of the HPT 2nd-stage air seal assembly.
The FAA determined it is not necessary to require use of specific service information as the visual inspection and FPI required by paragraph g1i of this AD are routine inspections that may vary between operators. The FAA, however, revised paragraph g1i of this AD to refer to Chapter 725260, Repair-01, of the PW2000 Series Engine Manual for guidance on striping the knife edge coating from the HPT 2nd-stage air seal assembly.

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Request To Remove FPI
Delta requested that paragraph g2ii of the NPRM paragraph g1ii of this AD remove the proposed requirement to perform an FPI
and require only visual inspections of the HPT 2nd-stage air seal assembly.
Delta reasoned that based on NDIP
1217, cracks are detectable by visual inspection, thereby making FPI
unnecessary. Delta concluded that performing only the visual inspection enables the HPT 2nd-stage air seal assembly to be inspected at initial disassembly while still in the presence of the mating HPT 1st-stage disk and HPT 2nd-stage hub, which simplifies determining if parts need to be scrapped if a crack is found. Otherwise, Delta stated that paragraph g1iii of the NPRM creates a logistical challenge for performing inspections as the HPT 2ndstage air seal assembly, mating HPT 1ststage disk, and HPT 2nd-stage hub could be routed to different locations with different lead times.
The FAA disagrees. While cracks may be detected by visual inspection, an FPI
will reveal cracks not detected by visual inspection. Additionally, the FPI is required to confirm that the HPT 2ndstage air seal assembly is free of cracks.
The FAA did not change this AD.
Request To Allow Repair of the HPT
2nd-Stage Air Seal Assembly Delta and MTU requested that paragraph g2ii of the NPRM
paragraph g1ii of this AD be updated to allow repair of the HPT 2ndstage air seal assembly if a crack is found. The commenters reasoned that Chapter 725260, Inspection/Check-01
and Repair-02, of the PW2000 Series Engine Manual provides information for repairing a cracked HPT 2nd-stage air seal assembly. The commenters concluded that this AD should allow repair; otherwise, Chapter 725260 of the PW2000 Series Engine Manual should be deleted or updated.
The FAA disagrees that the crack repairs identified in the engine manual should be incorporated in this AD. If a crack is found during the inspections required by this AD for the HPT 2ndstage air seal assembly, the part must be removed from service and cannot be repaired. The FAA disagrees that Chapter 725260 of the PW2000 Series Engine Manual should be deleted or updated. This repair is specifically for mechanical damage such as handling damage and foreign object damage in the knife edge area. This repair is not applicable to cracks identified by this AD. The damage addressed is unrelated and the repair does not need to be
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