Background \n\n\n\tThe FAA was notified by Boeing in March 2021 of a potential concern that the aft cargo compartment fire suppression capability is reduced on affected airplanes if the airplane is dispatched or released with failed electronic flow control of air conditioning packs, as is currently allowed by the existing FAA-approved MMEL of the affected airplane models. This MMEL allowance can result in the inability to contain a fire in the aft cargo compartment due to increased air leakage that degrades the fire suppression performance. A failed electronic flow control of air conditioning packs would significantly increase the pack airflow and cargo compartment air leakage. In April 2021, Boeing advised the FAA that such increased leakage could result in insufficient concentration of Halon fire suppressant in the aft cargo compartment, which can result in the inability to contain a fire for the time necessary to divert to a suitable airport. \n\tThe FAAis issuing this AD to address failed electronic flow control of air conditioning packs, which can result in an uncontained aft cargo compartment fire due to insufficient cargo fire suppression capability. The FAA is issuing this AD to address the unsafe condition on these products. \n\nFAA's Determination \n\n\n\tThe FAA is issuing this AD because the agency has determined the unsafe condition described previously is likely to exist or develop in other products of the same type design. \n\nAD Requirements \n\n\n\tThis AD prohibits dispatch or release of an airplane with cargo in the aft cargo compartment with failed electronic flow control of air conditioning packs. The AD specifically allows non-combustible and/or non-flammable empty cargo handling equipment, ballast, and/or fly-away kits in the aft cargo compartment. \n\nMMEL Revisions \n\n\n\tThis AD refers to items in ATA System No. 21, Air Conditioning, of Boeing 737 (B-737-100/200/300/400/500/600/700/800/900/900ER) MMEL, Revision 61, dated July 8, 2020; and Boeing 737 MAX (B-737-8/-8200/-9) MMEL, Revision 3, dated April 12, 2021; \1\ those items may also be included in an operator's FAA-approved minimum equipment list (MEL). This AD prohibits dispatch or release of the airplane under conditions currently allowed by those items in the MMEL. The FAA plans to revise the MMELs to modify those items; operators would then be required to also revise their applicable existing FAA-approved MEL accordingly. --------------------------------------------------------------------------- \n\n\n\t\1\ The MMEL items can be found in the applicable FAA-approved MMEL, which can be found on the Flight Standards Information Management System (FSIMS) website, https://fsims.faa.gov/PICResults.aspx?mode=Publication&doctype=MMELByModel. --------------------------------------------------------------------------- \n\nJustification for Immediate Adoption and Determination of the Effective Date \n\n\n\tSection 553(b)(3)(B) of the AdministrativeProcedure Act (APA) (5 U.S.C. 551 et seq.) authorizes agencies to dispense with notice and comment procedures for rules when the agency, for ''good cause,'' finds that those procedures are ''impracticable, unnecessary, or contrary to the public interest.'' Under this section, an agency, upon finding good cause, may issue a \n\n((Page 43405)) \n\nfinal rule without providing notice and seeking comment prior to issuance. Further, section 553(d) of the APA authorizes agencies to make rules effective in less than thirty days, upon a finding of good cause. \n\tAn unsafe condition exists that requires the immediate adoption of this AD without providing an opportunity for public comments prior to adoption. The FAA has found that the risk to the flying public justifies forgoing notice and comment prior to adoption of this rule because failed electronic flow control of air conditioning packs can result in an uncontained aft cargo compartment fire due to insufficient cargo fire suppression capability. Accordingly, notice and opportunity for prior public comment are impracticable and contrary to the public interest pursuant to 5 U.S.C. 553(b)(3)(B). \n\tIn addition, the FAA finds that good cause exists pursuant to 5 U.S.C. 553(d) for making this amendment effective in less than 30 days, for the same reasons the FAA found good cause to forgo notice and comment. \n\nComments Invited \n\n\n\tThe FAA invites you to send any written data, views, or arguments about this final rule. Send your comments to an address listed under ADDRESSES. Include Docket No. FAA-2021-0614 and Project Identifier AD- 2021-00831-T at the beginning of your comments. The most helpful comments reference a specific portion of the final rule, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may amend this final rule because of those comments. \n\tExcept for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to https://www.regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this final rule. \n\nConfidential Business Information \n\n\n\tCBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this AD contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this AD, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as ''PROPIN.'' The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this AD. Submissions containing CBI should be sent to Sam Nalbandian, Aerospace Engineer, Cabin Safety and Environmental Systems Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3993; email: Samuel.K.Nalbandian@faa.gov. Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking. \n\nRegulatory Flexibility Act \n\n\n\tThe requirements of the Regulatory Flexibility Act (RFA) do not apply when an agency finds good cause pursuant to 5 U.S.C. 553 to adopt a rule without prior notice and comment. Because the FAA has determined that it has good cause to adopt this rule without notice and comment, RFA analysis is not required. \n\nCosts of Compliance \n\n\n\tThe FAA estimates that this AD affects 663 airplanes of U.S. registry. \n\tThe FAA has determined that revising the operator's existing FAA- approved MEL, if accomplished in association with compliance for the requirements of this AD, would take an average of 90 work-hours per operator, although the agency recognizes that this number may vary from operator to operator. Since operators typically incorporate MEL changes for their affected fleets, the FAA has determined that a per-operator estimate is more accurate than a per-airplane estimate. Therefore, the FAA estimates the average total cost per operator to be $7,650 (90 work-hours x $85 per work-hour). \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 FAAwith 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, and \n\t(2) Will not affect intrastate aviation in Alaska. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.