Voglio sapere a riguardo di…

15792

Federal Register / Vol. 86, No. 56 / Thursday, March 25, 2021 / Rules and Regulations
BSI of the M-flange and added paragraph g2ii of this AD to clarify when to replace the diffuser case Mflange if the diffuser case M-flange CSN
are unknown or cannot be determined.
Request To Update Service Information IAE, MTU, and United requested that IAE Service Bulletin SB V2500ENG
720709, Revision 1, dated February 20, 2020 the SB, be referenced in this AD
instead of the Original Issue, dated December 13, 2019. United also requested that IAE NMASB V2500
ENG72A0706, Revision 2, dated November 7, 2019, be referenced.
The FAA partially agrees. Revision 2
of the NMASB was already referenced in the NPRM and, therefore, no change is needed to this AD. The FAA agrees to reference Revision 1 to the SB, which was issued after publication of the NPRM. The SB provides guidance on performing the replacement of the diffuser case M-flange and is not required for compliance with the AD.
Therefore, revising this AD to reference Revision 1 of the SB adds no additional burden on U.S. operators.
Request To Change Diffuser Case MFlange References IAE requested that the FAA change diffuser case M-flange to M-flange when referencing inspections. IAE
reasoned that inspection zone 2
includes all three flanges of the Mflange: Diffuser case M-flange, nozzle guide vane support, and the highpressure turbine HPT case forward flange, and all three flanges are required to be inspected.
The FAA agrees. The inspections are required on all surfaces of inspection zones 1, 2, and 3 of the M-flange. The FAA changed diffuser case M-flange to M-flange when referencing inspections throughout this AD. The FAA, however, did not change diffuser case M-flange when referencing replacement. Replacement of the diffuser case M-flange is the terminating action for the repetitive BSIs of the Mflange required by this AD.
Request for Credit for Diffuser Case MFlange Replacement Cathay, MTU, and WLFC requested credit for the replacement of the diffuser case M-flange if it was replaced before the effective date of this AD using TASK
724211300028, Repair-028
VRS3633, of the IAE V2500 Engine Manual VRS3633 Repair-028. Cathay and WLFC reasoned that the replacement of the diffuser case Mflange resets the M-flange cycles to zero.
Cathay and MTU cited the note to VRS3633 Repair-028 in the NMASB.

VerDate Sep<11>2014

16:53 Mar 24, 2021

Jkt 253001

Cathay also cited the note in the NMASB that fluorescent penetrant inspection FPI of the diffuser case Mflange bolt holes resets the cycles since the last FPI to zero.
The FAA disagrees with revising the Credit for Previous Actions section of this AD to give credit for replacement of the diffuser case M-flange using VRS3633 Repair-028. The FAA
determined that it is not necessary to provide previous credit for replacement of the diffuser case M-flange because this AD does not require use of specific service information to perform this replacement. The FAA revised paragraph i, Credit for Previous Actions, of this AD by removing references to providing credit for replacement of the diffuser case Mflange. If operators replaced the diffuser case M-flange prior to the effective date of this AD using any FAA-approved method, they meet the requirements of this AD under paragraph f of this AD.
Request To Clarify Major Mating Engine Flanges United requested that the FAA clarify the definition of engine shop visit and major mating engine flange. United asked if major flange aligns with the NMASB, which in Figure 1 of the NMASB, identifies the engine major flanges as H through P flanges. United also asked if the separation of pairs of major mating engine flanges includes the separation of H and J flanges when replacing damaged blades in HPC stages 3 through 6 during an HPC Surgical Strike Repair. If an engine shop visit includes separating flanges when performing an HPC Surgical Strike Repair, United requested that the FAA
update estimated costs of this AD to include costs associated with the teardown of modules.
The FAA agrees to clarify this definition of engine shop visit in this AD. The FAA has revised the definition of engine shop visit in this AD to refer to the induction of the engine into the shop for maintenance involving the separation of pairs of major mating engine flanges, KN. Based on this definition, separating H and J flanges during an HPC Surgical Strike Repair does not constitute an engine shop visit.
The FAA disagrees with updating the estimated costs of this AD. 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 inspect and replace the parts.

PO 00000

Frm 00014

Fmt 4700

Sfmt 4700

Request To Update Note to Paragraph g2
MTU requested that the FAA update Note 1 to paragraph g2i of this AD
to Instructions on performing the replacement of the diffuser case Mflange can be found in the Accomplishment Instructions, paragraphs 1.A. and B., of IAE SB
V2500ENG720709, Revision 1, dated February 20, 2020. MTU reasoned that the current wording suggests that there may be alternative instructions to replace the diffuser case M-flange other than the SB. MTU suggested that there are no alternatives to using IAE SB
V2500ENG720709 to replace the diffuser case M-flange. Therefore, MTU
notes that the language in the NPRM
may generate ambiguity.
The FAA disagrees. The SB is referenced in Note 2 to paragraph g2
of this AD as guidance for performing the replacement. The FAA is not mandating the use of a specific method to replace the diffuser case M-flange in this AD. The FAA did not change this AD based on this comment, but redesignated Note 1 to paragraph g2i in the NPRM to Note 2 to paragraph g2 in this AD based on the addition of a Note earlier in paragraph g of this AD.
Request To Include Diffuser Case Assembly P/Ns After Modification IAE requested that the FAA include the diffuser case assembly P/Ns, modified by the SB that are re-identified with new P/Ns after modification, and require replacement before the M-flange accumulates 20,000 CSN.
The FAA disagrees with including the list of diffuser case assembly P/Ns. The diffuser case M-flange, regardless of P/
N, must be replaced at the next engine shop visit after the effective date of this AD or before the M-flange accumulates 20,000 CSN, whichever occurs later.
Thereafter, the diffuser case M-flange must be replaced before accumulating 20,000 cycles since the previous replacement. Therefore, listing diffuser case assembly P/Ns is unnecessary.
Clarification to BSI Requirement The FAA determined the need to clarify the instructions required by paragraph g1iv of the NPRM. The NPRM referenced paragraphs 2.A.
through 2.G. of the NMASB to perform the BSI. However, paragraph 2.G. of the NMASB provides instructions to perform a FPI of the M-flange to confirm the indication as a crack. The FAA
added a note to paragraph g1iv of this AD to clarify that paragraph 2.G. of the NMASB describes procedures for
E:FRFM25MRR1.SGM

25MRR1