Discussion \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 The Boeing Company Model 787-8, 787-9, and 787-10 airplanes powered by Rolls Royce Trent 1000 engines. The NPRM published in the Federal Register on June 16, 2020 (85 FR 36352). The NPRM was prompted by reports of damage to the IFS forward upper fire seal and damage to thermal insulation blankets in the forward upper area of the TR. The NPRM proposed to require repetitive inspections of the IFS forward upper fire seal and thermal insulation blankets in the forward upper area of the TR for damage and applicable on-condition actions. \n\tThe FAA is issuing this AD to address damage to the IFS forward upper fire seal and the thermal insulation blankets of the TR due to airflow through structural gapping that could occur at the interface between the leading edge of the IFS and the engine splitter structure during flight. Failure of the IFS forward upper fire seal could cause the loss of seal pressurization and degrade the ability to detect and extinguish an engine fire, resulting in an uncontrolled fire. Damage to the TR insulation blanket could result in thermal damage to the TR inner wall, the subsequent release of engine exhaust components, and consequent damage to critical areas of the airplane. Furthermore, damage to the TR inner wall and IFS forward upper fire seal could compromise the integrity of the firewall and its ability to contain an engine fire, resulting in an uncontrolled fire. \n\n((Page 83756)) \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 for Clarification on Whether the Unsafe Condition is Likely To Exist on Other New Products \n\n\n\tAn individual commenter asked how likely it is that the same unsafe condition addressed in the proposed AD is to occur on other new products that are currently being evaluated for certification by the FAA, including the Boeing Model 777X. The commenter stated that the use of an electric thruster instead of a hydraulically-driven thrust reverser actuator would reduce the maintenance of a hydraulic system, and eliminate potential corrosion and fire risk. \n\tThe FAA agrees to clarify. As required by 14 CFR 21.21(b)(2), to certify an aircraft, the FAA must find that no feature or characteristic makes the aircraft unsafe. If the unsafe condition identified in this AD is determined to exist on any product that has not been certified by the FAA, the unsafe condition must be adequately addressed prior to FAA certification of that product. No change to this final rule is necessary in this regard. \n\nRequest for Explanation Regarding Timing of AD Action \n\n\n\tThe individual commenter asked why there was a 36 month period after August 27, 2018 (the effective date of AD 2018-15-03 Amendment 39-19335 (83 FR 34753, July 23, 2018) (AD 2018-15-03)), to take action on Boeing Alert Service Bulletin B787-81205-SB780033-00, Issue 001, dated November 1, 2017, which is required by AD 2018-15-03. The FAA infers that the commenter is referring to the 36-month compliance time for accomplishing the actions described in Boeing Alert Service Bulletin B787-81205-SB780033-00, Issue 001, dated November 1, 2017. The FAA also infers that the commenter is concerned regarding the time it took the FAA to take AD action to address the unsafe condition. \n\tThe FAA agrees to provide clarification regarding the timing of the publication of AD 2018-15-03 and the relationship between AD 2018-15-03 and this final rule. In the preamble of the NPRM preceding this final rule, the FAA stated that the proposed AD would not supersede or terminate any requirement of AD 2018-15-03. AD 2018-15-03 and this final rule both address damage to the IFS forward upper fire seal and damage to the thrust reverser thermal blanket. However, the damage to these areas is the result of two different causes. When the FAA developed AD 2018-15-03, that AD addressed the cause of damage that was identified at that time. The FAA assessed the level of risk and the compliance time, so that mandatory actions would be accomplished as soon as reasonably practical while maintaining an acceptable level of safety during the compliance period. The FAA determined that a compliance time of 36 months was adequate to address the unsafe condition identified in AD 2018-15-03. \n\tAfter AD 2018-15-03 was issued, Boeing identified an additional cause of the unsafe condition that was different from the one specified in AD 2018-15-03. This newly identified cause could similarly result in damage to the IFS forward upper fire seal and the thrust reverser thermal blanket. This final rule addresses the newly identified cause of the unsafe condition that was identified after AD 2018-15-03 was issued. As discussed in the preamble ofthe NPRM and the preamble of this final rule, the actions required by this final rule are interim action and the FAA may consider further rulemaking when a final corrective action becomes available. \n\tNo change to this final rule is necessary in regard to this comment. \n\nRequest for Clarification Regarding Inspection Personnel \n\n\n\tThe individual commenter also asked for clarification regarding what type of inspector would perform the inspections of the IFS forward upper fire seal and thermal blanket specified in the proposed AD. The commenter asked if the inspections would be performed by flight line inspectors or FAA inspectors. \n\tThe FAA agrees to provide clarification. The inspections required by this AD will be performed by qualified and certified maintenance personnel employed by airlines and airplane operators. No change to this final rule is necessary in this regard. \n\nRequest To Clarify the Unsafe Condition \n\n\n\tBoeing requested that the Discussion section and paragraph (e) of the proposed AD be revised to clarify the unsafe condition. The commenter stated that the unsafe condition statement in the proposed AD was not accurate. However, the commenter did not provide an explanation as to why the unsafe condition statement was not accurate. \n\tThe commenter indicated that in both the Discussion section and paragraph (e) of the proposed AD the explanation of the unsafe condition should be changed by removing the phrase ''the loss of seal pressurization'' from ''Failure of the IFS forward upper fire seal could cause the loss of seal pressurization and degrade the ability to detect and extinguish an engine fire, resulting in an uncontrolled fire,'' and replace it with the phrase ''excessive airflow into the core compartment firezone.'' \n\tThe commenter also requested that in both the Discussion section and paragraph (e) of the proposed AD the explanation of the unsafe condition be changed by removing the phrase ''the subsequent release of engine exhaust components, and consequent damage to critical areas of the airplane'' from ''Damage to the TR insulation blanket could result in thermal damage to the TR inner wall, the subsequent release of engine exhaust components, and consequent damage to critical areas of the airplane,'' and replace it with the phrase ''compromising the integrity of the firewall barrier which would increase the risk of an uncontained fire.'' \n\tThe FAA agrees with the commenter's request to clarify that damage to the TR inner wall could increase the risk of an uncontained fire. The FAA concurs that, depending on the level of damage to the TR inner wall and IFS forward upper fire seal, the capability of the firewall to contain an engine fire could be compromised, and therefore, it could result in an uncontrolled fire. The FAA also considers that damage to the IFS forward upper fire seal has the same effect. Although the FAA has already identified the potential for an uncontrolled fire as part of the unsafe condition addressed by this AD, the FAA has revised the Discussion section and paragraph (e) of this AD to provide additional clarification on this point. \n\tThe FAA disagrees with the commenter's request to remove the reference to ''loss of seal pressurization and'' from the description of the unsafe condition. This final rule addresses structural gapping that could occur between the leading edge of the IFS and the engine splitter structure during flight. Airflow through this structural gapping could damage the IFS forward upper fire seal and the thrust reverser thermal blanket. When the IFS forward fire seal is damaged, airflow can pass through the damaged areas of the IFS forward fire seal in addition to airflow through structural gapping, and this condition could further degrade the \n\n((Page 83757)) \n\nability to detect and extinguish an engine fire, and also damage the TR thermal blanket. The FAA's intent was to explain the effect of airflow through the damaged IFS forward fire seal due to loss of seal pressurization caused by the failure of the IFS forward upper fire seal. The FAA has not revised this AD in this regard. \n\tThe FAA also disagrees with the commenter's request to remove ''the subsequent release of engine exhaust components, and consequent damage to critical areas of the airplane'' from the description of the unsafe condition. The FAA has identified the potential of engine components departing the airplane due to damage to the TR inner wall as part of the unsafe condition addressed in this AD. This failure effect has been similarly discussed and addressed in a number of previously issued ADs including AD 2018-15-03, which is related to this AD. This AD has not been revised in this regard. \n\nRequest To Revise the Proposed Cost Estimates \n\n\n\tBoeing requested that the cost estimate in the NPRM be revised. Boeing stated that it initially communicated to the FAA that the manpower estimate of 0.5 man-hour for fire seal inspection and 0.5 man- hour for thermal blanket inspection was meant to be per engine, instead of per thrust reverser half as the FAA considered under the estimated cost provided in the NPRM. Boeing explained that the corrected manpower estimate for the fire seal inspection should be 0.25 man-hour per thrust reverser half, and the corrected manpower estimate for the thermal blanket inspection should be 0.25 man-hour per thrust reverser half. Boeing recommended that instead of 4 work-hours x $85 per hour = $340 per inspection cycle, the FAA update the labor cost for the inspection to 2 work-hours for a cost of $170 per inspection cycle. Boeing asserted that this would change the cost on U.S. operators to $2,380 per inspection cycle, based on 14 U.S. airplanes. \n\tThe FAA agrees with Boeing's observation that the cost estimate in the NPRM was incorrect based upon information that was incorrectly communicated from Boeing to the FAA. The FAA has revised the Costs of Compliance in this final rule. \n\nConclusionThe 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\tAre 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 than was already proposed in the NPRM. \n\tThe FAA 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 Boeing Alert Requirements Bulletin B787-81205- SB780041-00 RB, Issue 001, dated March 31, 2020. The service information describes procedures for repetitive inspections of the IFS forward upper fire seal and thermal insulation blankets of the TR for damage and applicable on-condition actions. Damage to a forward upper fire seal includes cuts, splits, nicks, punctures, and missing sections. Damage to an upper thermal blanket includes tears, cuts, missing metal skin, missing insulation, and over-temperature conditions shown by discoloration or scorching. The on-condition actions include replacing any damaged forward upper fire seal with a new fire seal having an appropriate part number, and replacing any damaged forward upper thermal blanket with a new thermal blanket. 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\nInterim Action \n\n\n\tThe FAA considers this AD interim action. If final action is later identified, the FAA might consider further rulemaking then. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 14 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD: \n\n\n\tEstimated Costs forRequired Actions ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Inspection..................... 2 work-hours x $85 per $0 $170 per $2,380 per \n\thour = $170 per inspection cycle. inspection cycle. \n\tinspection cycle. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe FAA estimates the following costs to do any necessary on- condition actions that would be required. The FAA has no way of determining the number of aircraft that might need these on-condition actions: \n\n\n\tEstimated Costs of On-Condition Actions ---------------------------------------------------------------------------------------------------------------- \n\tAction Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- Fire seal replacement............. 2 work-hours x $85 per $1,365 per TR half... $1,535 per TR half (4 TR \n\thour = $170 per TR half. halves per airplane). Thermal blanket replacement....... 1 work-hour x $85 per hour $17,855 per TR half.. $17,940 per TR half (4 TR \n\t= $85 per TR half. halves per airplane). ---------------------------------------------------------------------------------------------------------------- \n\n\n\tAccording to the manufacturer, some or all of the costs of this AD may be covered under warranty by Goodrich, thereby reducing the cost impact on affected individuals. The FAA does not control warranty coverage for affected individuals. As aresult, the FAA has included all known costs in the cost estimate. \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 \n\n((Page 83758)) \n\nthe 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\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 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.