SUPPLEMENTARY INFORMATION:

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2023-07-09, Amendment 39-22411 (88 FR 22895, April 14, 2023) (AD 2023-07-09). AD 2023-07-09 applied to certain Model 747-400 and -8 series airplanes. The NPRM was published in the Federal Register on July 9, 2026 (91 FR 42387). The NPRM was prompted by the manufacturer developing further action to address the unsafe condition. In the NPRM, the FAA proposed to require repetitive inspections for damage of the transfer pump housing inlet check valves and transfer pump motor impeller inlet adapters for the horizontal stabilizer fuel tank and applicable on-condition actions. The NPRM also proposed to limit the installation of affected parts under certain conditions. The FAA is issuing this AD to address the development of an ignition source within the horizontal stabilizer fuel tank resulting from wear to the transfer pump housing inlet check valves and transfer pump motor impeller inlet adapters of the horizontal stabilizer fuel tank. The unsafe condition, if not addressed, could, in combination with flammable fuel vapors, result in a fuel tank explosion and consequent loss of the airplane.

Discussion of Final Airworthiness Directive

Comments

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

The FAA received an additional comment from Turkish Airlines. The following presents the comments received on the NPRM and the FAA's response to each comment.

Request To Revise Applicability

Turkish Airlines requested that the FAA revise paragraph (c) of the proposed AD to be similar to the applicability of AD 2023-07-09 and to specify that airplanes equipped with an activated horizontal stabilizer fuel tank with Crane Aerospace Hydro-Aire horizontal stabilizer fuel transfer pump housings and transfer pump motor impellers are affected, instead of referencing Boeing Alert Requirements Bulletin 747-28A2373 RB, dated November 6, 2025 (Boeing Alert Requirements Bulletin 747-28A2373 RB), for identification information. Turkish Airlines stated that Boeing Alert Requirements Bulletin 747-28A2373 RB's effectivity identifies two configurations: (1) Model 747-400 and 747-8 airplanes equipped with activated horizontal stabilizer fuel tank with Crane Aerospace Hydro-Aire horizontal stabilizer fuel transfer pump housings and transfer pump motor impellers; and (2) Model 747-400 and 747-8 airplanes not equipped with an activated horizontal stabilizer fuel tank with Crane Aerospace Hydro-Aire horizontal stabilizer fuel transfer pump housings and transfer pump motor impellers. Turkish Airlines added that no action is required for airplanes in the second configuration.

The FAA disagrees. Determining whether an airplane was included in AD 2023-07-09's applicability required an examination of each airplane's configuration to determine whether the AD applied to that airplane, regardless of whether the airplane was determined to be affected by the AD's requirements. Boeing Alert Requirements Bulletin 747-28A2373 RB contains a definitive list of all airplanes that could be affected by the unsafe condition and requires an examination of their configuration. While either approach would produce an acceptable outcome, in this situation, referring to the service information to determine applicability is clearer and consistent with the principle that only airplanes to which the AD applies are subject to the requirements of this AD. No change to this AD has been made in this regard.

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. None of the changes will increase the economic burden on any operator.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 747-28A2373 RB, dated November 6, 2025. This material specifies procedures for repetitive detailed inspections of the transfer pump housing inlet check valves and transfer pump motor impeller inlet adapters for any damage and applicable on-condition actions. On-condition actions include replacing the damaged transfer pump housing inlet check valve with a new or serviceable transfer pump housing inlet check valve (Option 1), or replacing the affected transfer pump housing with a transfer pump housing containing a new or serviceable transfer pump housing inlet check valve (Option 2); and replacing an affected transfer pump motor impeller with a new or serviceable transfer pump motor impeller.

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.

Interim Action

The FAA considers this AD to be an interim action. The main and center wing tanks utilize the same pump design but are currently not subject to the same unsafe condition due to the shutoff logic of the pumps. However, if further analysis or reports related to the main or center tank pumps change this assessment, the FAA might consider further rulemaking for those tanks.

Costs of Compliance

The FAA estimates that this AD affects 31 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD: ( printed page 68881)

The FAA estimates the following costs to do any necessary replacements that would be required based on the results of the proposed inspection. The agency has no way of determining the number of aircraft that might need these replacements:

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,

(2) Will not affect intrastate aviation in Alaska, and

(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.

The Amendment

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