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Federal Register / Vol. 86, No. 120 / Friday, June 25, 2021 / Rules and Regulations NPRM published in the Federal Register on September 24, 2020 85 FR
60103. The NPRM was prompted by a report from the manufacturer that an inspection had found two stages 610
compressor rotor spools in the HPC
assembly damaged at similar locations on the webs. The subsequent investigation determined that tool marks were created during the manufacturing process. In addition, the manufacturer also reported that certain stages 610
compressor rotor spool webs did not undergo a required FPI during production.
In the NPRM, the FAA proposed to require inspection of the stages 610
compressor rotor spool. Operators of certain affected GEnx1B or GEnx2B
model turbofan engines have already completed acceptable inspections of the aft web of stage 6, stage 7, and stage 8
of the stages 610 compressor rotor spool. The FAA proposed to require operators of those affected engines to complete the inspection of the stages 6
10 compressor rotor spool no later than the next engine shop visit. The FAA
proposed to require all other remaining affected GEnx1B and GEnx2B model turbofan engines to complete this inspection by the next engine shop visit, before the stages 610 compressor rotor spools accumulate 6,500 cycles since new, or before further flight if 6,500
cycles since new has already been accumulated as of the effective date of this AD. Depending on the results of the inspection, the FAA proposed to require replacement of the stages 610
compressor rotor spool with a part eligible for installation. The FAA is issuing this AD to address the unsafe condition on these products.

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Discussion of Final Airworthiness Directive Comments The FAA received comments from seven commenters. The commenters were American Airlines American, GE
Aviation, Japan Airlines, Nippon Cargo Airlines NCA, the Air Line Pilots Association, International, United Airlines Engineering, and Boeing Commercial Airplanes. Three commenters supported the proposed rule without change. One commenter requested that the FAA add a term to the Definitions paragraph of the proposed rule, and use the latest version of the service information. Three commenters requested certain clarifications or changes to the Required Actions and Previous Credit sections.
The following presents the comments received on the NPRM and the FAAs response to each comment.

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Request To Clarify Rejectable Indication GE Aviation requested that the FAA
define the term rejectable indication to avoid confusion in the event an indication is found during inspection.
GE Aviation requested that the FAA
define rejectable indication as an indication that does not meet the serviceable or repairable limits defined in the special procedure referenced in GE GEnx1B Service Bulletin SB 72
0472 R02, dated November 5, 2020
GEnx1B SB 720472 and GE GEnx 2B SB 720415 R02, dated November 5, 2020 GEnx2B SB 720415.
The FAA agrees to define a rejectable indication as used in paragraph g2
of the Required Actions section of this AD and added the definition in paragraph h, Definitions, of this AD.
Request To Clarify Acceptance of Reworked Parts American requested that the FAA
clarify paragraph g2 and paragraph i, Credit for Previous Actions, regarding installation of parts that initially failed inspection with a rejectable indication but were later reworked and found acceptable.
American stated that GE has been accepting parts that were reworked using GE Subtask 720000210012 in the GEnx1B EM 720000, Special Procedure 023, in accordance with approved GE Departure Recommendations.
The FAA disagrees. Paragraph g2
of this AD requires that if during an inspection, a stages 610 compressor rotor spool is found to have a rejectable indication, as defined in paragraph h of this AD, then the stages 610
compressor rotor spool must be removed from service. If the stages 610
compressor rotor spool is subsequently repaired or reworked, operators would need to submit an alternative methods of compliance AMOC request to the FAA to allow use of the repaired or reworked stages 610 compressor rotor spool.
Request To Revise References to Service Bulletin GE Aviation requested that the FAA
update the specified service information by referencing Revision 2 of GE GEnx 1B SB 720472 and GE GEnx2B SB 72
0415. GE noted that Revision 2 of these SBs had not been issued at the time of publication of the NPRM.
The FAA agrees and has updated this AD to reference GEnx1B SB 720472
R02 and GEnx2B SB 720415 R02, both dated November 5, 2020. This change to this AD imposes no additional burden on operators.

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Request To Revise Previous Credit Japan Airlines requested that the FAA
grant credit for the borescope inspection BSI or eddy current inspection ECI
required by paragraph g1 of this AD
if inspections were previously performed in accordance with GE
GEnx1B SB 720472 R01, dated July 24, 2020.
The FAA agrees and has updated paragraph i, Credit for Previous Actions, to allow credit for inspections performed using GE GEnx1B SB 72
0472 R01, dated July 24, 2020 or GE
GEnx2B SB 720415 R01, dated July 24, 2020, as applicable.
Request for Reference Date Clarification NCA requested that the FAA clarify the meaning of previously undergone in paragraph g1ii of this AD. NCA
commented that one of its engines underwent an inspection during an engine shop visit using GEnx2B SB 72
0385 R02, dated July 29, 2019 and GE
GEnx2B SB 720398 R00, dated October 30, 2019, before the effective date of this AD but after publication of GEnx2B SB 720415 R01. NCA noted that the reference to previously undergone means that it has been implemented in accordance with SB in the past without any specific timeframe, so it is not clear if the NCAs engine can apply the no cycles since new CSN
limit.
The FAA clarified paragraph g1i and ii of this AD by removing the phrase previously undergone and referring instead to engines that have undergone inspections before the effective date of this AD.
Change to Compliance Time The FAA updated Table 1 to paragraph g1 of this AD by allowing operators 100 flight cycles to perform the inspections required by paragraph g1 of this AD when an engine has a stages 610 compressor rotor spool with 6,400 CSN or greater as of the effective date of this AD. This change allows operators a grace period to complete the required inspections without unnecessary grounding of airplanes and still meets the safety intent of this AD.
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.

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