AD 2021-16-08 Requires Replacement Of Affected Rotating Air HPT Front Seals

The FAA is superseding Airworthiness Directive (AD) 2019-12-05 for certain CFM International S.A. (CFM) CFM56-5B, CFM56-5C, and CFM56-7B model turbofan engines with a certain rotating air high-pressure turbine (HPT) front seal. AD 2019-12-05 required replacement of the affected rotating air HPT front seal with a part eligible for installation.

This AD was prompted by cracks found in the rotating air HPT front seal. This AD requires replacement of affected rotating air HPT front seals installed on CFM CFM56-5B, CFM56-5C, and CFM56-7B model turbofan engines that have fewer cycles since being reconfigured than the engines affected by AD 2019-12-05. This AD also requires CFM56-5B or CFM56-7B model turbofan engines with a reconfigured rotating air HPT front seal that was previously operated in a CFM56-5C model turbofan engine to follow the removal requirements for the CFM56-5C model turbofan engine. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective September 28, 2021.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2019-12-05, Amendment 39-19660 (84 FR 28717, June 20, 2019), (AD 2019-12-05).

AD 2019-12-05 applied to all CFM CFM56-5B, CFM56-5C, and CFM56-7B model turbofan engines with a certain rotating air HPT front seal. AD 2019-12-05 required replacement of the affected rotating air HPT front seal with a part eligible for installation. The actions required by AD 2019-12-05 were interim and only addressed the highest risk engines with an affected rotating air HPT front seal that have a specified number of cycles since being reconfigured.

The NPRM published in the Federal Register on October 23, 2019 (84 FR 56709). AD 2019-12-05 was prompted by cracks found in the rotating air HPT front seal. In the NPRM, the FAA proposed to retain the requirements of AD 2019-12-05 and extend those requirements to engines that have fewer cycles since being reconfigured.

After the NPRM was issued, CFM revised its service information that provides instructions for replacing the affected rotating air HPT front seal. In addition, the revised service information addresses CFM56-5B or CFM56-7B model turbofan engines with a reconfigured rotating air HPT front seal that was previously operated in a CFM56-5C model turbofan engine, and specifies that those engines follow the removal limits established for CFM56-5C model turbofan engines. In addition, the FAA determined changes to the proposed AD were necessary based on comments received on the NPRM.

Accordingly, the FAA issued a supplemental notice of proposed rulemaking (SNPRM), which published in the Federal Register on March 23, 2021 (86 FR 15436). In the SNPRM, the FAA proposed to retain the requirements of AD 2019-12-05 and expand the applicability to require the replacement of affected rotating air HPT front seals installed on CFM CFM56-5B, CFM56-5C, and CFM56-7B model turbofan engines that have fewer cycles since being reconfigured than the engines affected by AD 2019-12-05. In the SNPRM, the FAA also proposed to require that CFM56-5B and CFM56-7B model turbofan engines with a reconfigured rotating air HPT front seal that was previously operated in a CFM56-5C model turbofan engine follow the removal requirements of the CFM56-5C model turbofan engine. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov