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 RRD Trent 1000-AE3, Trent 1000-CE3, Trent 1000-D3, Trent 1000-G3, Trent 1000-H3, Trent 1000-J3, Trent 1000-K3, Trent 1000-L3, Trent 1000-M3, Trent 1000-N3, Trent 1000-P3, Trent 1000-Q3, Trent 1000-R3, Trent 7000-72, and Trent 7000-72C model turbofan engines. The NPRM published in the Federal Register on April 2, 2020 (85 FR 18478). The NPRM was prompted by a report of crack findings in the front air seal on the IPC shaft assembly during the stripping of a flight test engine. The NPRM proposed to require initial and repetitive BSIs of the IPC shaft assembly and, depending on the results of the inspection, replacement of the IPC shaft assembly with a part eligible for installation. The FAA is issuing this AD to address the unsafe condition on these products. \n\tThe European Union Aviation Safety Agency (EASA), which is the Technical Agent for the Member States of the European Community, has issued EASA AD 2019-0282, dated November 20, 2019 (referred to after this as ''the MCAI''), to address the unsafe condition on these products. The MCAI states: \n\n\n\tAn occurrence was reported of finding cracks in the front air seal of the IPC shaft assembly during stripping of a flight test engine. Follow-up inspections of other in-shop engines revealed two more cracked front air seals of IPC shaft assemblies. \n\tThis condition, if not detected and corrected, could lead to IPC shaft failure, possibly resulting in engine in-flight shut-down and consequent reduced control of the aeroplane. \n\tTo address this potential unsafe condition, Rolls-Royce developed an inspection method and issued the NMSB, providing those inspection instructions. \n\tFor the reason described above, this (EASA) AD requires repetitive on-wing inspections of the front air seal of the affected part at a specific area between the fourth (rearmost) sealfin of the IPC shaft assembly front air seal and the IPC Stage 1 disc and, depending on findings, removal from service of the engine for corrective action(s). \n\n\n\tYou may obtain further information by examining the MCAI in the AD docket on the internet at https://www.regulations.gov by searching for and locating Docket No. FAA-2020-0293. \n\nComments \n\n\n\tThe FAA gave the public the opportunity to participate in developing this final rule. The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nRequest To Update Methods To Gain Access to the IPC Shaft Assembly \n\n\n\tDelta Air Lines (DAL) requested that paragraph (g)(1), Required Actions, of this AD be updated to specify that gaining access to the front air seal of the IPC shaft assembly to perform the BSI can be accomplished through the engine inlet and low-pressure compressor (LPC) fan blades or through the outlet guide vanes (OGVs) regardless of whether the BSI of the front air sealis performed concurrently with any other inspections. \n\tDAL cited paragraph 3.B.(2)(b) of Rolls-Royce Trent 1000 Alert Non- Modification Service Bulletin (NMSB) 72-AK451, Initial Issue, dated November 14, 2019 (''the NMSB''), that states that accessing the front air seal may be made through the OGVs ''if performed concurrently with IP Compressor Stage 1 blade inspections.'' As a result, inspectors may have less difficulty accessing the inspection area through the OGVs. Further, DAL reasoned that tooling for entry through the OGVs might be more readily available in certain stations where the affected aircraft operate. \n\tThe FAA agrees that access to the front air seal of the IPC shaft assembly can be accomplished through the engine inlet and LPC fan blades or through the OGVs regardless of any other inspections occurring at the time. The FAA, however, disagrees with updating paragraph (g)(1) of this AD because this AD does not require a certain method to access the front air seal ofthe IPC shaft assembly. \n\nRequest To Remove Engine To Allow for Verification of Cracks \n\n\n\tDAL requested that the FAA update paragraph (g)(3), Required Actions, of this AD to require removal of the engine before further flight and to allow verification of any cracks prior to mandating replacement of the IPC shaft assembly. DAL added that the EASA AD, which states to remove of the engine from service if any crack is detected and to contact RRD for approved corrective actions, allows for the possibility that an engine can be removed from the aircraft and then subsequently cleared for continued service after cleaning and reassessment of a suspected indication. \n\tThe FAA disagrees with updating paragraph (g)(3) of this AD to require removal of the engine. While the engine can be removed from the aircraft and subsequently cleared for continued service after cleaning and reassessment, the engine does not need to be removed from the aircraft to verify a crack. According to the Accomplishment Instructions, paragraph 3.B.(2)(e), of the NMSB, if a crack is found, it is permissible to clean the suspected area and then repeat the BSI or visual inspection of the IPC shaft assembly. Therefore, no change to this AD is required. \n\nRequest To Allow Visual Inspections of the IPC Shaft Assembly During a Shop Visit \n\n\n\tDAL requested that the FAA update paragraph (g)(2), Required Actions, of this AD to allow credit for an IPC shaft assembly that received the BSI using the NMSB or a general visual inspection during an engine shop visit. DAL reasoned that when the IPC shaft assembly is exposed during an engine shop visit, the inspection area can be accessed without a borescope. \n\n((Page 62977)) \n\n\n\tThe FAA agrees that visual inspections using standard shop procedures would provide an equivalent level of safety as an on-wing BSI if the front air seal of the IPC shaft assembly is exposed. The FAA updated paragraph (g)(2) of this AD to allow a visual inspection using FAA-approved maintenance procedures if the part is exposed. \n\nRequest To Revise Definition of Part Eligible for Installation \n\n\n\tDAL requested that the FAA update the definition of a ''part eligible for installation'' be revised to also include a part that has been inspected per standard shop procedures. DAL reasoned that paragraph (h) of the NPRM only defined a part eligible for installation to include a new IPC shaft assembly or an IPC shaft assembly that, before installation, passed an inspection in accordance with referenced service information, which only includes an on-wing BSI and does not allow for inspection during an engine shop visit. Therefore, paragraph (h) of the NPRM, as written, allows only for the reinstallation of the IPC shaft assembly that had been previously inspected on-wing before removal from an engine. Additionally, DAL noted that both the RRD Trent 1000 and Trent 7000 Cleaning, Inspection, and Repair Manuals, Section 72-32-31, provide standard manual procedures for identifying cracks on the IPC shaft assembly. \n\tThe FAA agrees and updated the definition of a ''part eligible for installation'' in paragraph (h)(2) of this AD to include an in-shop BSI and visual inspection using FAA-approved maintenance procedures. \n\nRequest To Remove Reference to Table of Inspection Intervals \n\n\n\tDAL requested that the FAA update paragraph (g)(2), Required Actions, of this AD to remove the reference to Table 1 to paragraph (g)(1) for inspection intervals. DAL suggested that the FAA mirror the language of the MCAI that states that in-shop inspections ''may be substituted for any on-wing BSI as required by paragraph (1) of this (EASA) AD, provided the compliance time is not exceeded.'' DAL reasoned that Table 1 to paragraph (g)(1) of the NPRM includes only the initial inspection intervals, and therefore could be interpreted to exclude substitution for repetitive inspections. \n\tThe FAA agrees that Table 1 to paragraph (g)(1) of this AD provides the compliance time for the initial inspection, whereas paragraph (g)(1) of this AD requires repetitive inspections at stated intervals. The FAA updated paragraph (g)(2) of this AD from ''may be substituted for any on-wing BSI, provided the compliance time specified in Table 1 to paragraph (g)(1) of this AD is not exceeded'' to ''may be substituted for any on-wing BSI, provided the compliance time specified in paragraph (g)(1) of this AD is not exceeded.'' \n\nSupport for the AD \n\n\n\tThe Boeing Company expressed support for the AD as written. \n\nConclusion \n\n\n\tThe FAA reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this final rule with the changes described previously and minor editorial changes. The FAA has determined that these minor changes: \n\t(Agr)re consistent with the intent that was proposed in the NPRM for addressing the unsafe condition; and \n\tDo not add any additional burden upon the public thanwas already proposed in the NPRM. \n\tThe FAA has also determined that these changes will not increase the economic burden on any operator or increase the scope of this final rule. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tThe FAA reviewed Rolls-Royce Trent 1000 Alert NMSB 72-AK451, Initial Issue, dated November 14, 2019. The Alert NMSB describes procedures for initial and repetitive BSIs of the IPC shaft assembly. This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 14 engines installed on airplanes of 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\tActionLabor cost Parts cost product operators ---------------------------------------------------------------------------------------------------------------- BSI or visual inspection of IPC 3.5 work-hours x $85 per $0 $297.50 $4,165 \n\tshaft assembly. hour = $297.50. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe FAA estimates the following costs to do any necessary replacement that are required based on the results of the mandated inspection. The FAA has no way of determining the number of engines that might need this replacement: \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Replace IPC shaft assembly................ 1,080 work-hours x $85 per hour = $1,365,219 $1,457,019 \n\t$91,800. ---------------------------------------------------------------------------------------------------------------- \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 \n\n((Page 62978)) \n\nnecessary 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\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 among the various levels of government. \n\tFor the reasons discussed above, I certify 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 byreference, Safety.