SUPPLEMENTARY INFORMATION:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all The Boeing Company Model 777-200, -200LR, -300, -300ER, and 777F series airplanes. The NPRM was published in the Federal Register on November 17, 2025 (90 FR 51216). The NPRM was prompted by a report from an operator of a fire in the MLG wheel well on a Model 777 airplane. A subsequent investigation found that the cause of the fire was an overheated ACMP. Further investigation found that a lock washer and nut were missing from a moving contact in the related electrical load control unit (ELCU). The missing lock washer and nut left the main contact operator bar unrestrained and in a position that let two-phase power go to the ACMP, which caused the ACMP to overheat, leak hydraulic fluid, and subsequently start a fire in the MLG wheel well. As a result, the design of the ACMP has been modified to include fusible links as a new feature to prevent the ACMP overheat if one of the electrical phases fails. Additionally, the manufacturer has determined that part number (P/N) 731966 on continuous two-phase power application may cause the pump to overheat and ignite a fire in the wheel well. P/N 731966 can be subjected to a single failure of the ELCU that results in continuous two-phase power application with no ability to remove power. In the NPRM, the FAA proposed to require a records check or inspection for any installed ACMP with a certain part number and applicable on-condition actions. The FAA is issuing this AD to address a single failure of the ELCU in the ACMP. This condition, if not addressed, could result in the ACMP overheating and igniting a fire in the wheel well and consequent damage to the airplane, loss of continued safe flight and landing and/or personnel injury.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from Boeing and the Air Line Pilots Association, International (ALPA) who supported the NPRM without change.

The FAA also received comments from Air Canada, American Airlines (American), FedEx, the Citizens Rulemaking Alliance, and United Airlines (United). The following presents those comments and the FAA's response.

Request To Delay Issuance of the AD

United requested that the FAA either delay issuance of the proposed AD until related ADs for the Boeing Model 757 and Model 767 airplanes are ready for publication or assist Boeing with expediting the release of the applicable service bulletins for those airplane models, which United said were scheduled to be released in the second quarter of 2026. United stated it operates Boeing Model 757, 767, and 777 airplanes that all utilize ACMP P/N 731966, and that the new ACMP P/N 3033115-100 is currently applicable only to the Model 767 and Model 777 airplanes, while the Model 757 airplanes are limited to ACMP P/N 731966. United Airlines stated this could create an internal compliance challenge due to the inability to fully transition away from ACMP P/N 731966 since that part is required for the Model 757 airplanes.

The FAA acknowledges the commenter's concern but disagrees with the request. The FAA has determined that it is necessary to prohibit installation of any affected part on any Model 777 airplane as of the effective date of this AD, and that delaying issuance of this AD would allow affected parts installed on affected airplanes before the effective date of this AD to remain on those airplanes longer, which could affect the safety of the affected fleet. Further, the FAA does not consider it appropriate to delay issuance while awaiting new service information for other airplane models that are not applicable to this AD. However, Boeing recently released the service bulletins for the Model 757 and Model 767, including the Model 747, airplanes in March 2026 allowing operators to bring their entire fleet into compliance. The FAA may issue additional rulemaking mandating these service bulletins. The FAA did not change this AD as a result of this comment.

Request To Add Grace Period for Part Installation Prohibition

American requested that the FAA revise paragraph (i) of the proposed AD to include a 6-month grace period before the parts installation prohibition becomes effective. American stated that a 6-month grace period, representing approximately 10 percent of the total compliance time, would allow operators to obtain sufficient inventory of upgraded ACMPs to support airplane operational requirements and reduce the risk of part shortages in the event of in-service failures. American also noted that Boeing Fleet Team Digest (FTD) 777 FTD-29-21001, referenced in Boeing Alert Service Bulletin 777-29A0047, dated September 11, 2025, incorporates steps into the aircraft maintenance manual requiring an ELCU installation test at all locations where an ELCU is removed or installed, which would validate the integrity and safe operation of the ELCU providing power to ACMP P/N 731966.

The FAA acknowledges American's concern but disagrees with the request. ACMP P/N 731966 can be modified to the new acceptable ACMP configuration in accordance with the Eaton Aerospace service information referenced in Boeing Alert Requirements Bulletin 777-29A0047 RB, dated September 11, 2025. Therefore, the FAA has determined that sufficient parts should be available to support compliance with the requirements of this AD. In addition, including a grace period increases the possibility that an affected part could be installed on an airplane after the effective date of this AD. The FAA did not change this AD as a result of this comment.

Request To Use an Alternative Part Number

FedEx requested that the FAA revise paragraph (h)(2) of the proposed AD to include ACMP P/N 66133-04 as an ( printed page 61129) acceptable replacement part for P/N 3033115-100. FedEx stated that the Boeing 777 illustrated parts catalog (IPC) identifies multiple ACMP part numbers as eligible for installation, including P/N 66133-04, which is an earlier version of P/N 66133-06. FedEx noted P/N 66133-04 has been installed on several of its affected airplanes because the IPC shows it is an eligible alternative.

The FAA disagrees with the request. Although ACMP P/N 66133-04 is not subject to the identified unsafe condition, the FAA has determined that installation of that part is not acceptable for compliance with this AD. In a separate investigation that was not determined to be a safety issue, P/N 66133-04 was found not to comply with certain certification requirements. P/N 66133-06 is the redesigned ACMP that complies with those certification requirements. Boeing has informed the FAA that references to the interchangeability of P/N 3033115-100 with P/N 66133-04 will be removed from future revisions of the IPC. Although the FAA has not mandated the removal of, or prohibited the installation of, P/N 66133-04, it is not appropriate to specify that part as an acceptable replacement for compliance with this AD. The FAA did not change this AD as a result of this comment.

Request To Revise the Applicability of the Parts Installation Prohibition

FedEx requested that the FAA revise paragraph (i) of the proposed AD to state that ACMP P/N 731966 may not be installed on any “Boeing Model 777 series” airplane, instead of “any airplane.” FedEx stated the phrase “on any airplane” could be interpreted as prohibiting the installation of P/N 731966 on all airplane models. FedEx noted there are currently 433 ACMPs having P/N 731966 installed on its fleet of Boeing Model 757 and Model 767 airplanes, and it does not have sufficient spare P/N 3033115-100 or approved alternatives available for replacement on those airplanes.

The FAA disagrees with the request. No change is necessary because the requirements of this AD, including the parts prohibition in paragraph (i), apply only to the airplanes identified in paragraph (c) of this AD.

Request To Clarify Compliance Time for the Parts Installation Prohibition

Air Canada requested clarification as to whether paragraph (i) of the proposed AD would require replacement of an already installed ACMP having P/N 731966 as of the effective date of the AD, or whether the prohibition would apply only to new installations occurring after the effective date. As an example, the commenter asked whether a serviceable P/N 731966 may be installed on an airplane if there is a maintenance emergency that requires replacement of an ACMP after the AD is effective but before the 60-month compliance time required by the AD.

The FAA provides the following response. If an ACMP having P/N 731966 has been installed on an airplane identified in paragraph (c) of this AD before the effective date of this AD, it must be replaced within 60 months after the effective date of this AD. However, any ACMP installed on any airplane after the effective date of this AD must be an acceptable part number. In the commenter's example, a serviceable P/N 731966 may not be installed on the airplane.

Request To Justify Forgoing Notice and Comment or Issue an NPRM

The Citizens Rulemaking Alliance requested that the FAA either provide its justification for finding good cause to bypass notice and comment procedures, or convert this action to an NPRM with a 30- to 60-day comment and delay the effective date for airplanes not at immediate risk. The commenter asserted the FAA has not adequately justified use of the good cause exemption to bypass notice and comment and the 30-day delayed effective date.

The FAA notes the comment was submitted in response to an NPRM for which the FAA provided a 45-day comment period. This final rule is effective 35 days after its publication in the Federal Register . Therefore, no change to this AD is necessary.

Request To Make Incorporation by Reference (IBR) Materials Reasonably Available

The Citizens Rulemaking Alliance requested that the FAA make IBR material available and free to the public during the comment period and add the IBR materials to the AD docket.

In the preamble of the NPRM, the FAA notified the public that the IBR material would be available for review under Docket No. FAA-2025-3997 at regulations.gov. This material was posted to the AD docket on November 17, 2025. Therefore, no change to this AD is necessary.

Request To Comply With the Paperwork Reduction Act (PRA)

The Citizens Rulemaking Alliance requested that the FAA revise the AD to confirm that the AD complies with the PRA. If the AD does not comply with the PRA, the commenter requested that the FAA remove or stay any reporting requirements until the AD complies with the PRA.

The FAA notes this AD does not require reporting. If an AD were to require reporting, the preamble of the AD would include a paragraph titled “Paperwork Reduction Act” that would provide the applicable OMB control number, required PRA statements, and the estimated time to collect the required information (burden). Any costs associated with the reporting requirement would be included in the Costs of Compliance section in the preamble of the AD. Therefore, the FAA did not change this AD as a result of this comment.

Request To Consider Impact on Small Entities

The Citizens Rulemaking Alliance requested that the FAA either prepare an initial regulatory flexibility analysis, or provide the factual basis for its conclusion that the AD will not have a significant economic impact on a substantial number of small entities.

The FAA has considered the AD's impact on small businesses and provides the following factual basis for its RFA certification.

The Regulatory Flexibility Act of 1980, Pub. L. 96-354, 94 Stat. 1164 (5 U.S.C. 601-612), as amended by the Small Business Regulatory Enforcement Fairness Act of 1996 (Pub. L. 104-121, 110 Stat. 857, Mar. 29, 1996) and the Small Business Jobs Act of 2010 (Pub. L. 111-240, 124 Stat. 2504, Sept. 27, 2010), requires Federal agencies to consider the effects of the regulatory action on small business and other small entities and to minimize any significant economic impact. The term “small entities” comprises small businesses and not-for-profit organizations that are independently owned and operated and are not dominant in their fields, and governmental jurisdictions with populations of less than 50,000.

Need for and Objectives of the Rule

The FAA is adopting a new AD for all The Boeing Company Model 777-200, -200LR, -300, -300ER, and 777F series airplanes. This AD was prompted by a report of an overheated ACMP that caused a fire in the MLG wheel well. This AD requires a records check or inspection for any installed ACMP with a certain part number and applicable on-condition actions. This AD also prohibits the installation of affected parts. The FAA is issuing this AD to address the unsafe condition on these products. ( printed page 61130)

Small Entities to Which the Rule Will Apply

The FAA used the definition of small entities in the RFA for this analysis. The RFA defines small entities as small businesses, small governmental jurisdictions, or small organizations. In 5 U.S.C. 601(3), the RFA defines “small business” to have the same meaning as “small business concern” under section 3 of the Small Business Act. The Small Business Act authorizes the Small Business Administration (SBA) to define “small business” by issuing regulations.

The SBA (2023) has established size standards for various types of economic activities, or industries, under the North American Industry Classification System (NAICS). These size standards generally define small businesses based on the number of employees or annual receipts. The following table shows the SBA size standards for all industries with at least one (1) impacted entity.^[1] Note that the SBA definition of a small business applies to the parent company and all affiliates as a single entity.

To identify small entities, the FAA first identified the primary NAICS of the entity or parent company, and then used data from different sources ( e.g., company annual reports, Bureau of Transportation Statistics) to determine whether the entity meets the applicable size standard. The following table provides a summary of the results.

Projected Reporting, Recordkeeping, and Other Compliance Requirements

The FAA estimates affected entities will incur an inspection cost of $170 per airplane. Based upon the results of the inspection, operators could incur replacement costs of $77,099. If an operator were to incur all inspection and replacement costs, the FAA estimates each operator would incur $77,269 per airplane. The FAA analyzes the cost of inspection costs as the low case for each small entity. The high case includes both inspection and replacement costs for each small entity. The following table displays the small entity case burdens percentage for compliance based on annual revenue for each operator and their associated NAICS industry.

Significant Alternatives Considered

The FAA is adopting a new AD for all The Boeing Company Model 777-200, -200LR, -300, -300ER, and 777F series airplanes. This AD was prompted by a report of an overheated ACMP that caused a fire in the MLG wheel well. This AD requires a records check or inspection for any installed ACMP with a certain part number and applicable on-condition actions. This AD also prohibits the installation of affected parts. No alternatives were considered as the FAA is issuing this AD to address the unsafe condition on these products.

Request To Provide Additional Cost Information

The Citizens Rulemaking Alliance requested that the FAA add to the docket the economic analysis underlying the FAA's determination that the AD is not significant under Executive Order 12866 and not applicable to the Unfunded Mandates Reform Act. The commenter stated the cost analysis should include the number of affected U.S.-registered airplanes, labor hour assumptions, parts costs, expected airplane downtime, and aggregate costs.

In the Costs of Compliance section of the proposed AD, the FAA disclosed the number of affected airplanes on the U.S. registry, estimated number of work hours and parts costs provided by the manufacturer, and the aggregate costs. Additionally, the FAA considered the impact that this AD will have on affected operators and determined this AD will not trigger any downtime costs because the requirements of this AD can be performed during regularly scheduled maintenance.

Further, the FAA has determined that the current labor rate of $85 per hour remains accurate for this AD. The FAA evaluates this rate periodically, based on U.S. Department of Labor Statistic (BLS) data found at data.bls.gov/​oes, and will change the rate when appropriate. The FAA used a blended wage rate to estimate the labor rate for this AD, where the FAA assumes 60 percent weight for aircraft mechanics (at a fully burdened mean wage rate of $69.85 per hour) and 40 percent for general and operations managers (at a fully burdened mean wage rate of $108.15 per hour). To calculate the blended wage rate, the FAA multiplied each wage rate by its corresponding weight and added up the products to obtain a wage rate of $85.17, which the FAA rounded down to $85.

Since the FAA has assessed and disclosed all known costs of the AD requirements in the Costs of Compliance section of the proposed AD, and the commenter did not provide additional cost data for the FAA to consider in its cost analysis, the FAA determined that the existing analysis is complete. Based upon the analysis provided throughout the proposed AD and in the previous comment response, the FAA certifies that this AD is not a “significant regulatory action” under Executive Order 12866. The FAA did not change this AD as a result of this comment.

Conclusion

The 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, this AD is adopted as proposed in the NPRM.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 777-29A0047 RB, dated September 11, 2025. This material specifies procedures for a records check or inspection for any installed ACMP with P/N 731966 and applicable on-condition actions. On-condition actions include replacing any ACMP P/N 731966 with ACMP P/N 3033115-100 or later approved ACMP part number at affected locations. This material 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.

Costs of Compliance

The FAA estimates that this AD affects 334 airplanes of U.S. registry, and that the inspection/records review is required for 290 of those airplanes. The FAA estimates the following costs to comply with this AD:

The 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 this replacement: ( printed page 61132)

The FAA has included all known costs in its cost estimate. According to the manufacturer, however, some or all of the costs of this AD may be covered under warranty, thereby reducing the cost impact on affected operators.

Authority for This Rulemaking

Title 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.

The 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.

Regulatory Findings

This 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.

For the reasons discussed above, I certify that this AD:

(1) Is not a “significant regulatory action” under Executive Order 12866, and

(2) Will not affect intrastate aviation in Alaska.

The Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows:

91 FR 61127