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Federal Register / Vol. 86, No. 54 / Tuesday, March 23, 2021 / Proposed Rules Request To Clarify Engine and Rotating Air HPT Front Seal Intermix Requirements
HPT front seal with a part eligible for installation.
Actions Since the NPRM Was Issued Since the FAA issued the NPRM, CFM has issued CFM Service Bulletin SB CFM565B S/B 721074, Revision 02, dated November 6, 2019; CFM SB
CFM565C S/B 720794, Revision 02, dated November 6, 2019; and CFM SB
CFM567B S/B 721042, Revision 02, dated November 6, 2019. These SBs provide service information for following the removal limits established for CFM565C model turbofan engines for CFM565B or CFM567B model turbofan engines with a reconfigured rotating air HPT front seal that was previously operated in a CFM565C
model turbofan engine.
Comments The following discussion presents the comments received on the NPRM and the FAAs response.
Request To Revise and Remove Installation Prohibition American Airlines, CFM, and Lufthansa Technik AG requested the FAA revise the language in the Installation Prohibition to specify that it is only applicable to those rotating air HPT front seals that have affected serial numbers S/Ns. Lufthansa Technik AG
also requested the FAA remove the Installation prohibition from this proposed rule. Lufthansa Technik AG
indicated that this AD already requires the removal of rotating air HPT front seals at an interval that will prevent an unsafe condition.
The FAA partially agrees. The FAA
has revised this proposed AD by adding language to the Installation Prohibition referencing the specific S/Ns in the Applicability section to ensure that the rotating air HPT front seals affected by the Installation Prohibition are clear.
The FAA disagrees with the request to remove the Installation Prohibition. The requirement to remove rotating air HPT
front seals is necessary to address the unsafe condition and provide a drawdown period to remove the affected rotating air HPT front seals from service.
Rotating air HPT front seals installed on a different HPT disk from which they were removed after the effective date of the AD will not meet the certified removal limits established in the Airworthiness Limitations Section.

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American Airlines requested the FAA
clarify the engine and rotating air HPT
front seal intermix requirements, since CFM has released SB revisions that provide guidance on rotating air HPT
front seals that have been operated in multiple engine models.
The FAA agrees and has revised this proposed AD. The FAA revised the compliance requirements in this proposed AD by adding additional required actions for CFM565C model turbofan engines with an affected rotating air HPT front seal that was assembled to a second or later HPT disk since being reconfigured.
Request To Specify No Reporting Requirement American Airlines requested the FAA
add a paragraph to this proposed AD to specify that there are no reporting requirements. The commenter noted that the CFM SBs specify reporting information to CFM.
The FAA disagrees. The required actions of this AD do not mandate the use of the referenced service information to comply with this AD.
The reporting instructions included in the SBs are not required by this AD. The FAA made no change to this AD.
Request To Clarify Inclusion of Engine Models Lufthansa Technik AG requested the FAA provide clarification regarding the NPRM supersedure preambles discussion of expanding the applicability of the AD to include CFM565B, CFM565C, and CFM567B
model turbofan engines. The commenter indicated that those engine models are already included in applicability of the AD 20191205.
The NPRM supersedure preamble states that AD 20191205 only addresses the highest risk engines with an affected rotating air HPT seal that has a specified number of cycles since being reconfigured. The NPRM supersedure proposes to expand the affected engine models to include all CFM CFM565B, CFM565C, and CFM567B model turbofan engines, including those engines that have fewer cycles since being reconfigured. The NPRM
supersedure does not propose the addition of affected engine models to the applicability. The FAA made no change to this proposed AD.

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FAAs Determination The FAA is proposing this AD after determining the unsafe condition described previously is likely to exist or develop in other products of the same type design. Certain changes described above expand the scope of the NPRM.
As a result, it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this SNPRM.
Related Service Information The FAA reviewed CFM Service Bulletin SB CFM565B S/B 721074, Revision 02, dated November 6, 2019;
CFM SB CFM565C S/B 720794, Revision 02, dated November 6, 2019;
and CFM SB CFM567B S/B 721042, Revision 02, dated November 6, 2019.
CFM SB CFM565B S/B 721074, Revision 02, describes procedures for replacement of the affected rotating air HPT front seal on CFM CFM565B
model turbofan engines. CFM SB
CFM565C S/B 720794, Revision 02, describes procedures for replacement of the affected rotating air HPT front seal on CFM CFM565C model turbofan engines. CFM SB CFM567B S/B 72
1042, Revision 02, describes procedures for replacement of the affected rotating air HPT front seal on CFM CFM567B
model turbofan engines.
Proposed AD Requirements in This SNPRM
This proposed AD would retain the requirements of AD 20191205 84 FR
28717, June 20, 2019 AD 20191205.
The proposed AD would expand the applicability to require the replacement of affected rotating air HPT front seals installed on CFM CFM565B, CFM56
5C, and CFM567B model turbofan engines that have fewer cycles since being reconfigured than the engines affected by AD 20191205. This proposed AD would also require CFM565B and CFM567B model turbofan engines with a reconfigured rotating air HPT front seal that was previously operated in a CFM565C
model turbofan engine to follow the removal requirements of the CFM565C
model turbofan engine.
Costs of Compliance The FAA estimates that this AD, if adopted as proposed, would affect four engines installed on airplanes of U.S.
registry.
The FAA estimates the following costs to comply with this proposed AD:

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