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AGENCY:
Federal Aviation Administration (FAA), DOT.
ACTION:
Final rule.
SUMMARY:
The FAA is adopting a new airworthiness directive (AD) for certain The Boeing Company Model 777 airplanes. This AD was prompted by a determination that the nitrogen enriched air distribution system (NEADS) cover plate assembly attached to a certain vent stringer in the center wing tank was installed without a designed electrical bond. This AD requires installing electrical bonding and grounding, installing the cover plate assembly with new fasteners, and revising the existing maintenance or inspection program, as applicable, to incorporate new airworthiness limitations. The FAA is issuing this AD to address the unsafe condition on these products.
DATES:
This AD is effective October 15, 2024.
The Director of the Federal Register approved the incorporation by reference of a certain publication listed in this AD as of October 15, 2024.
ADDRESSES:
AD Docket: You may examine the AD docket at regulations.gov under Docket No. FAA-2024-0761; 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 address for Docket Operations is U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
Material Incorporated by Reference:
- For Boeing material identified in this AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Boulevard, MC 110-SK57, Seal Beach, CA 90740-5600; telephone 562-797-1717; websitemyboeingfleet.com.
- You may view this material at the FAA, Airworthiness Products Section, Operational Safety Branch, 2200 South 216th St., Des Moines, WA. For information on the availability of this material at the FAA, call 206-231-3195. It is also available atregulations.gov under Docket No. FAA-2024-0761.
FOR FURTHER INFORMATION CONTACT:
Anthony Decaro, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; telephone: 562-627-5374; email: Anthony.D.Decaro@faa.gov.
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 certain The Boeing Company Model 777 airplanes. The NPRM published in the Federal Register on March 25, 2024 (89 FR 20555). The NPRM was prompted by a report indicating a production audit by the design approval holder found that the design of the NEADS cover plate assembly did not comply with the requirements for nitrogen generation system certification (14 CFR 25.981). It was discovered that the NEADS cover plate assembly attached to a certain vent stringer in the center wing tank was installed without a designed electrical bond for electrostatic dissipation. In the NPRM, the FAA proposed to require installing electrical bonding and grounding, installing the cover plate assembly with new fasteners, and revising the existing maintenance or inspection program, as applicable, to incorporate new airworthiness limitations. The FAA is issuing this AD to address the accumulation of electrostatic charge in the cover plate assembly and float valve assembly during airplane refueling, which could lead to electrostatic discharge to the surrounding structure. The unsafe condition, if not addressed, could result in result in an ignition source inside the fuel tank and subsequent fire or explosion.
Discussion of Final Airworthiness Directive
Comments
The FAA received a comment from the Air Line Pilots Association, International (ALPA) who supported the NPRM without change and a comment from United Airlines who reviewed the NPRM and provided no additional comment. The FAA received an additional comment from Boeing. The following presents the comment received on the NPRM and the FAA's response to that comment.
Request To Clarify the Unsafe Condition
Boeing requested the unsafe condition be revised to clarify when the accumulation of electrostatic charge on the vent float valve assembly could occur. Specifically, Boeing requested adding the words “during airplane refueling” to the unsafe condition because the threat of accumulation is only present during refueling operation when charged fuel is introduced to the fuel tank from the airport refueling infrastructure, and that other airplane operations such as flight do not introduce a threat to the installation.
The FAA agrees with clarifying the unsafe condition. The FAA has revised the Background section and paragraph (e) to clarify that the FAA is issuing this AD to address the accumulation of electrostatic charge in the cover plate assembly and float valve assembly during airplane refueling, which could lead to electrostatic discharge to the surrounding structure.
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, and any other changes described previously, 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 777-47A0007 RB, dated November 21, 2023. This material specifies procedures for removing the cover plate assembly and its attached float valve assembly, installing electrical bonding and grounding, measuring the bonding resistance between the bolt heads/cover plate assembly/float valve assembly mounting flange and the vent stringer No. 15 and between the nuts and the cover plate assembly, and installing the cover plate assembly with new fasteners. This material also specifies revising the operator's maintenance or inspection program, as applicable, by incorporating new airworthiness limitations (AWLs). 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 292 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD:
Estimated Costs
| Action | Labor cost | Parts cost | Cost per product | Cost on U.S. operators |
|---|---|---|---|---|
| Electrical bond installation | 27 work-hours × $85 per hour = $2,295 | $93 | $2,388 | $697,296 |