Background \n\n\n\tThe FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all General Electric Company (GE) CF6-80A, CF6-80A1, CF6-80A2, CF6-80A3, CF6-80C2A1, CF6- 80C2A2, CF6-80C2A3, CF6-80C2A5, CF6-80C2A5F, CF6-80C2A8, CF6-80C2B1, CF6-80C2B1F, CF6-80C2B1F1, CF6-80C2B1F2, CF6-80C2B2, CF6-80C2B2F, CF6- 80C2B3F, CF6-80C2B4, CF6-80C2B4F, CF6-80C2B5F, CF6-80C2B6, CF6-80C2B6F, CF6-80C2B6FA, CF6-80C2B7F, CF6-80C2B8F, CF6-80C2D1F, CF6-80C2K1F, and CF6-80C2L1F model turbofan engines. The NPRM published in the Federal Register on February 22, 2021 (86 FR 10496). The NPRM was prompted by an inspection by the manufacturer that revealed cracking of the HPT rotor stage 1 disk caused by increased stress on the HPT rotor stage 1 disk as a result of flange-to-flange cracking on the HPT thermal shield. In the NPRM, the FAA proposed to require visual inspection and FPI of the HPT thermal shield and, if cracking isdetected, removal from service of the HPT thermal shield, HPT rotor stage 1 disk and HPT rotor stage 2 disk. The FAA is issuing this AD to address the unsafe condition on these products. \n\nDiscussion of Final Airworthiness Directive \n\nComments \n\n\n\tThe FAA received comments from five commenters. The commenters were Atlas Air, Boeing Commercial Airplanes (Boeing), Delta Air Lines (Delta), United Airlines (United) and the Air Line Pilots Association, International (ALPA). The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nRequest To Update Shop Manual \n\n\n\tAtlas Air requested that the FAA revise GE CF6-80C2, ESM 72-53-05, High Pressure Turbine (HPT) Rotor Thermal Shield--Inspection to add the proposed requirement to remove from service the HPT thermal shield, the HPT rotor stage 1 disk, and the HPT rotor stage 2 disk from service if a crack is found, since the thermal shield can be sent to different vendors outside the engine shop. Delta also suggested that the technical data within the Engine Shop Manual (ESM) should be updated to ensure inspection requirements are equivalent across all tasks within the ESM. \n\tThe FAA disagrees. Requiring updates to the ESM is unnecessary to correct the unsafe condition identified in this AD. The visual and FPI inspections in the required actions of this AD are the necessary actions to correct the unsafe condition. Operators, at their discretion, may work with the original equipment manufacturer to suggest changes to the ESM to include the inspections required by this AD. \n\n((Page 38913)) \n\nRequest To Revise References to Engine Manual \n\n\n\tBoeing requested that the FAA update reference to the service information in the Related Service Information section of the NPRM by referencing Revision 90 of the GE CF6-80A Engine Manual and Revision 91 of the CF6-80C2 Engine Manual. These revisions of the respective engines manuals include updated procedures regarding HPT rotor Stage 1 and Stage 2 disk serviceability for these model engines with respect to HPT thermal shield inspection findings. \n\tThe FAA agrees and has updated the Related Service Information section of this AD as suggested by the commenter. \n\nRequest To Clarify Inspection Instructions \n\n\n\tDelta requested that the FAA clarify that the mandated visual and FPI inspections should be accomplished in accordance with the engine manual for the affected engine models. \n\tThe FAA disagrees. Operators may use any approved method to perform the visual and FPI inspections required by this AD. \n\nRequest To Clarify Engine Applicability \n\n\n\tUnited requested that the FAA remove CF6-80C2B8F model turbofan engines from the applicability of this AD. United commented that two HPT thermal shield configurations exist, part number (P/N) 2787M85P01 and P/N 9315M41P20. Neither of these configurations are applicable to the R88DT HPT rotor installed on CF6-80C2B8F model turbofan engines. United requested that if the FAA considers the CF6-80C2B8F turbofan engine model affected by this AD, then the applicable engine manual should be updated to reflect the inspections required by this AD. \n\tThe FAA agrees. This AD is not applicable to the R88DT HPT rotor installed on CF6-80C2B8F model turbofan engines because that rotor configuration does not have an affected thermal shield. The FAA added the applicable part numbers for HPT thermal shields installed on CF6- 80A and CF6-80C2 model turbofan engines to the applicability paragraph of this AD. \n\nSupport for the NPRM \n\n\n\tALPA supported the NPRM without change. \n\nConclusion \n\n\n\tThe 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. None of the changes will increase the economic burden on any operator. \n\nRelated Service Information \n\n\n\tThe FAA reviewed ESM 72-53-00 High Pressure Turbine Rotor Assembly--Disassembly (CF6-80A ESM 72-53-00), dated February 15, 2020 from the GE CF6-80A Engine Manual GEK72501--Rev 90, dated February 15, 2021. CF6-80A ESM 72-53-00 describes procedures for the removal of the HPT thermal shield, the HPT rotor stage 1 disk, and the HPT rotor stage 2 disk installed on CF6-80A model turbofan engines. \n\tThe FAA also reviewed ESM 72-53-00 High Pressure Turbine Rotor Assembly--Disassembly (CF6-80C2 ESM 72-53-00), dated December 1, 2019 from the GE CF6-80C2 Engine Manual GEK92451--Rev 91, dated December 1, 2020. CF6-80C2 ESM 72-53-00 describes procedures for the removal of the HPT thermal shield, the HPT rotor stage 1 disk, and the HPT rotor stage 2 disk installed on CF6-80C2 model turbofan engines. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 1,084 engines installed on airplanesof U.S. registry. \n\tThe FAA estimates the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per Cost on U.S. \n\tAction Labor cost Parts cost product operators ---------------------------------------------------------------------------------------------------------------- Perform FPI and visual inspection of 2 work-hours x $85 per $0 $170 $184,280 \n\tHPT thermal shield. hour = $170. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe FAA estimates the following costs to do any necessary replacements that would be required based on the results of the inspection. The agency has no way of determining the number of aircraft that might need these replacements. \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Replace HPT thermal shield.................... 2 work-hours x $85 per hour = $209,600 $209,770 \n\t$170. Replace HPT rotor stage 1 disk................ 2 work-hours x $85 per hour = 799,700 799,870 \n\t$170. Replace HPT rotor stage 2 disk................ 2 work-hours x $85 per hour = 364,600 364,770 \n\t$170. ---------------------------------------------------------------------------------------------------------------- \n\nAuthority for This Rulemaking \n\n\n\tTitle 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority. \n\tThe FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. \n\n((Page 38914)) \n\nRegulatory Findings \n\n\n\tThis AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities amongthe various levels of government. \n\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\t(2) Will not affect intrastate aviation in Alaska, and \n\t(3) Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.