Airworthiness Directives; The Boeing Company Airplanes
This document has a comment period that ends in 44 days. (04/10/2026)AGENCY:
Federal Aviation Administration (FAA), DOT.ACTION:
Final rule; request for comments.
SUMMARY:
The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 737-8, 737-9, and 737-8200 airplanes. This AD was prompted by reports of in-flight events of excessive cabin and flight deck temperatures that could not be controlled by the flightcrew using existing procedures. This AD requires revising the existing airplane flight manual (AFM) to provide the flightcrew with operating procedures (non-normal checklists) if a certain circuit breaker in the standby power control unit (SPCU) trips. The FAA is issuing this AD to address the unsafe condition on these products.
DATES:
This AD is effective February 24, 2026.
The FAA must receive comments on this AD by April 10, 2026.
ADDRESSES:
You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:
- Federal eRulemaking Portal: Go to regulations.gov. Follow the instructions for submitting comments.
- Fax: 202-493-2251.
- Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
- Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
AD Docket: You may examine the AD docket at regulations.gov by searching for and locating Docket No. FAA-2026-1332; or in person at Docket Operations between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this final rule, any comments received, and other information. The street address for Docket Operations is listed above.
FOR FURTHER INFORMATION CONTACT:
Derrick Herrera, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 817-222-5140; email: derrick.r.herrera@faa.gov.
SUPPLEMENTARY INFORMATION:
Comments Invited
The FAA invites you to send any written data, views, or arguments about this final rule. Send your comments using a method listed under the ADDRESSES section. Include Docket No. FAA-2026-1332 and Project Identifier AD-2026-00084-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.
Except 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 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.
Confidential Business Information
CBI 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 Derrick Herrera, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 817-222-5140; email: derrick.r.herrera@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.
Background
The FAA has received two reports of in-flight events of excessive cabin and flight deck temperatures that could not be controlled by the flightcrew using existing procedures. An investigation found these events resulted from the BAT BUS SECT 2 circuit breaker (CB3062) on the SPCU tripping. The SPCU gives automatic and manual control of the battery and standby buses. The BAT BUS SECT 2 provides power to air conditioning and cabin pressure functions, including the left and right pack flow control valve solenoids (On/Off), left and right pack overheat protection circuits, zone supply duct overheat protection circuits, and cabin pressure manual mode control. The BAT BUS SECT 2 circuit breaker trip causes an unintended erroneous electrical ground signal to the smart ram air door actuators (SRADAs), which in turn causes both ram air deflector doors to extend (close), thus reducing cooling airflow to the air conditioning heat exchangers. The reduced airflow causes insufficient cooling of the hot bleed air, which causes both packs to supply excessively hot air to the cabin and flight deck. This air conditioning system malfunction could cause an uncontrollable, excessively high temperature in the cabin and flight deck. This condition, if not addressed, could lead to injury or incapacitation of flightcrew and passengers, which could result in the inability to maintain safe flight and landing. The FAA is issuing this AD to address the unsafe condition on these products.
Explanation of Existing AFM Procedures and Procedures Required by This AD
This AD provides flightcrew procedures for a controlled descent, an attempt to reset the tripped BAT BUS SECT 2 circuit breaker and, if that attempt is unsuccessful, selecting engine bleed switches OFF. This AD includes three AFM procedures, one of which is revised (Cabin Temperature Hot procedure) as shown in Appendix 1 of this AD, another of which is new (Cabin Temperature Hot BAT BUS Sect 2 Circuit Breaker Trips procedure) as shown in Appendix 2 of this AD, and the other procedure currently exists in the quick reference handbook (QRH) but not in the existing AFM (PACK procedure) as shown in Appendix 3.
FAA's Determination
The 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.
AD Requirements
This AD requires revising the Operating Procedures section of the existing AFM to provide the flightcrew with non-normal checklists if the BAT BUS SECT 2 circuit breaker in the SPCU trips.
Interim Action
The FAA considers this AD to be an interim action. An assessment of the SPCU found that two environmental control system (ECS) circuit breakers (C262 and C263) downstream of the SPCU may also trip. The FAA is considering further rulemaking to provide flightcrew procedures for addressing tripped ECS circuit breakers. Additionally, the manufacturer is currently developing a modification to address the unsafe condition identified in this AD. Once this modification is developed, FAA-approved, and available, the FAA might consider additional rulemaking.
Justification for Immediate Adoption and Determination of the Effective Date
Section 553(b) of the Administrative Procedure 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 final 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.
An 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 a tripped BAT BUS SECT 2 circuit breaker, and resulting effects on the cabin environment that cannot be controlled via normal procedures, could lead to injury or incapacitation of flightcrew and passengers, which could result in the inability to maintain safe flight and landing. Additionally, the compliance time in this AD is shorter than the time necessary for the public to comment and for publication of the final rule. Accordingly, notice and opportunity for prior public comment are impracticable and contrary to the public interest pursuant to 5 U.S.C. 553(b).
In 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.
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