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Federal Register / Vol. 86, No. 142 / Wednesday, July 28, 2021 / Rules and Regulations
prohibited. The requirements contained in this AD take precedence over any contrary provisions in the manufacturers instructions for continued airworthiness. The FAA did not update this AD.
Request To Clarify Removal From Service Delta requested that the FAA clarify paragraph g2ii of the NPRM
paragraph g1ii of this AD that states the HPT 2nd-stage air seal assembly must be removed from service if a crack is found. Delta asked if the HPT 2nd-stage air seal assembly must be scrapped, or if the HPT 2nd-stage air seal assembly can be repaired and returned to service after re-identifying it with a new P/N. Delta added that the engine manual provides a repair option of knife-edge cracks caused by mechanical damage.
The FAA notes that remove from service in this AD indicates that the HPT 2nd-stage air seal assembly should be permanently removed from service if a crack is found. Any cracked HPT 2ndstage air seal assembly cannot be repaired and returned to service per the requirements of this AD.

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Request To Remove Before Further Flight FedEx requested that the FAA remove the phrase before further flight from paragraphs g2ii and iii of the NPRM paragraphs g1ii and iii of this AD. FedEx reasoned that since the visual inspection, knife edge coating removal, and FPI are performed at every piece-part opportunity of the mating HPT 1st-stage disk, HPT 2nd-stage disk, or the HPT 2nd-stage air seal assembly, before further flight is redundant.
Additionally, FedEx stated that the overhaul facility must comply with the engine manual inspection criteria and would have no other option but to make the HPT 2nd-stage air seal assembly permanently unserviceable.
The FAA agrees and removed before further flight from paragraphs g1ii and iii of this AD.
Request To Clarify Part Replacement After Crack Is Found MTU requested clarification regarding whether the mating HPT 1st-stage disk or HPT 2nd-stage hub needs to be replaced if a crack is found after performing the inspections proposed by paragraph g2iii of the NPRM
paragraph g1iii of this AD, or if both the mating HPT 1st-stage disk and HPT 2nd-stage hub need to be replaced.
If a crack is found as identified in the shaded region of Figure 1 to paragraph g1iii of this AD Figure 1 that
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extends toward the knife-edge region of the HPT 2nd-stage air seal assembly, this AD requires replacement of the HPT
2nd-stage air seal assembly, mating HPT
1st-stage disk, and HPT 2nd-stage hub.
Request To Clarify Terminating Action UAL requested clarification if paragraph h, Terminating Action, of the NPRM applies to the visual inspection and FPI of the HPT 2nd-stage air seal assembly proposed by paragraph g2 of the NPRM paragraph g1 of this AD.
The FAA notes that there is no terminating action to the visual inspection and FPI of the HPT 2nd-stage air seal assembly required by paragraph g1 of this AD. The visual inspection and FPI required by paragraph g1 of this AD are required for all HPT 2ndstage air seal assemblies, including P/Ns others than 1A8209 or 1A8209001. As stated in an earlier response, with the removal of the BSI requirements from this AD, the FAA removed the terminating action from this AD.
Request To Clarify Applicability for Visual Inspection and FPI
UAL requested clarification of whether paragraph g1 of this AD
applies if an HPT 2nd-stage air seal assembly, with a P/N other than P/N
1A8209 or 1A8209001, is installed.
Delta requested that an applicability statement referencing P/Ns for affected HPT 2nd-stage air seal assemblies be added to paragraph g2 of the NPRM.
Paragraph g2 of the NPRM proposed to require a visual inspection of the HPT
2nd-stage air seal assembly, stripping the knife edge coating from the HPT
2nd-stage air seal assembly, and then performing an FPI of the HPT 2nd-stage air seal assembly. Delta noted that if an HPT 2nd-stage air seal assembly has been modified and re-identified with a new P/N using PW SB PW2000 72754, Revision No. 2, dated April 30, 2019, then it should not be subject to the same inspections as HPT 2nd-stage air seal assembly, P/N 1A8209 or 1A8209001.
The FAA disagrees and notes that the visual inspection and the FPI required by paragraph g1i of this AD are required for all HPT 2nd-stage air seal assemblies, regardless of the P/N. The FAA did not update this AD.
Request To Allow Installation of Mating Parts Without Past HPT 2nd-Stage Air Seal Assembly Inspection Verification Delta requested that a mating HPT 1ststage disk and HPT 2nd-stage hub made serviceable before the effective date of this AD be eligible for installation without verification that all past HPT
2nd-stage air seal assemblies had visual
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inspections and FPI to verify no cracks were found. Delta reasoned that the inspections were not previously required and adequate records may not exist. Additionally, Delta stated it might not be possible to re-inspect all previous HPT 2nd-stage air seal assemblies for cracks as some may have been scrapped before the inspection.
The FAA notes that an HPT 1st-stage disk and HPT 2nd-stage hub made serviceable before the effective date of this AD are not subject to the requirements of g1iii of the AD
until their next piece part exposure. The FAA did not update this AD.
Request To Clarify the Location of the Forward and Aft Edges Delta and MTU requested that the FAA clarify the location of the forward and aft edges of the HPT 2nd-stage air seal assembly. Delta asked if the forward edge is the barrel section forward of the 1 knife-edge or any part that extends beyond the barrel section.
The FAA removed references to forward edge and aft edge of the HPT 2nd-stage air seal assembly from this AD. In their place, the FAA added Figure 1 to paragraph g1iii of this AD to specify the locations of the HPT
2nd-stage air seal assembly that require inspection for cracks.
Request To Clarify the Definition of Through-Crack Delta and FedEx requested that the FAA clarify the definition of throughcrack. Delta asked if a through-crack is a crack going through the axial direction or radial direction of the HPT
2nd-stage air seal assembly. Delta referenced Figure 5 of NDIP1217 that appears to show a through-crack in the axial direction. Delta inferred from paragraph i4 of the NPRM that a through-crack is in the radial direction.
Delta requested a diagram to help illustrate what constitutes a throughcrack.
FedEx stated that a lenticular seal is a two-piece component that becomes an inseparable assembly during manufacturing. As a result, it would be impossible to distinguish a throughcrack from a surface crack over a large area of the HPT 2nd-stage air seal assemblys exterior since its interior surfaces are inaccessible. FedEx cited Chapter 725260, Inspection/Check 01, Figures 801 and 801A, of the PW2000 Series Engine Manual, which highlights areas where throughthickness cracks are critical. According to FedEx, however, these images fail to address the ability to determine whether a surface crack is a through-crack.
Additionally, the PW2000 Series Engine
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