2024-06522. Airworthiness Directives; The Boeing Company Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 777 airplanes. This proposed AD was prompted by a report indicating multiple findings of cracks in the fuselage skin common to the underwing longeron (UWL). This proposed AD would require external or internal (depending on configuration) inspections for any cracking of the left and right side fuselage skin common to the UWL, and applicable on-condition actions. The FAA is proposing this AD to address the unsafe condition on these products.

DATES:

The FAA must receive comments on this proposed AD by May 13, 2024.

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: [phone].

• 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 under Docket No. FAA-2024-0769; 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 NPRM, any comments received, and other information. The street address for Docket Operations is listed above.

Material Incorporated by Reference:

• For service information identified in this NPRM, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone [phone]; website myboeingfleet.com.

• You may view this service information 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 at regulations.gov by searching for and locating Docket No. FAA-2024-0769.

FOR FURTHER INFORMATION CONTACT:

Luis Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail].

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments to an address listed under ADDRESSES . Include “Docket No. FAA-2024-0769; Project Identifier AD-2023-00556-T” at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, 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 proposal 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 NPRM.

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 NPRM 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 NPRM, 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 NPRM. Submissions containing CBI should be sent to Luis Cortez-Muniz Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail]. 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 reports indicating multiple findings of cracks in the fuselage skin common to the UWL on all series of Boeing Model 777 airplanes. The crack findings were made during UWL replacement or accomplishing Boeing Service Bulletins 777-53-0084 or 777-53-0087, or Boeing Requirements Bulletin 777-57A0122 RB. In many of the fuselage skin crack reports, the UWL was reported not damaged. The found fuselage skin cracks were hidden externally by the UWL, and internally by fuselage frames and stringers. The fuselage skin cracks were found on airplanes with as few as 2,000 total flight cycles and 18,000 total flight hours. These fuselage skin cracks were determined to be caused by cold work surface upset that is not removed from the mating parts and high joint load transfer or significant local bending stresses at critical fastener locations. These conditions, if not addressed, could result in an inability of a principal structural element (PSE) to sustain limit load, leading to reduced structural integrity of the airplane and possible loss of control of the airplane.

Boeing has issued Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, to address the identified unsafe condition.

Other Relevant Rulemaking

AD 2023-17-14, Amendment 39-22541 (88 FR 60111, August 31, 2023) (AD 2023-17-14) requires repetitive inspections for cracking of the left and right side ring chords, repair angles, front spar lower chords, and front spar webs (depending on configuration) common to the UWL located at station (STA) 1035; modification of the front spar lower chord for some airplanes; repetitive post-modification inspections; and applicable on-condition actions, as specified in Boeing Alert Requirements Bulletin 777-57A0122 RB, dated October 8, 2021; and requires a maintenance records review of previously modified airplanes for the procedures used during that modification, and applicable corrective actions. Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, specifies that the modification in Boeing Alert Requirements Bulletin 777-57A0122 RB should be done before further flight if cracking is found during certain inspections. Therefore, this proposed AD, which mandates Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, might require that the modification be done prior to the compliance time for that modification as specified in AD 2023-17-14. For airplanes on which a front spar lower chord modification specified in Boeing Alert Requirements Bulletin 777-57A0122 RB is done as part of the requirements of paragraph (g) of this proposed AD, the modification requirements of paragraph (g) of AD 2023-17-14 are terminated for the applicable side (left or right) on which the modification was done.

AD 2019-11-02, Amendment 39-19648 (84 FR 28722, June 20, 2019) (AD 2019-11-02) requires repetitive inspections of the left and right side UWLs and applicable on-condition actions as specified in Boeing Alert Service Bulletin 777-53A0081, Revision 2, dated March 29, 2019. The accomplishment of the longeron modification specified in Boeing Service Bulletin 777-53-0084, Revision 2, dated December 9, 2020, or Boeing Service Bulletin 777-53-0087, Revision 1, dated March 4, 2020; or the front spar lower chord modification specified in Boeing Alert Requirements Bulletin 777-57A0122 RB, dated October 8, 2021; which must be done if cracking is found during certain inspections specified in Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, terminates the inspection requirements of paragraph (g) of AD 2019-11-02 for the applicable side (left or right) on which the modification was done.

FAA's Determination

The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023. This service information specifies procedures for external or internal (depending on configuration) detailed and ultrasonic or surface high frequency eddy current (HFEC) inspections for any cracking of the left and right side fuselage skin common to the UWL, and applicable on-condition actions. On-condition actions include, among other things, modification of the fuselage skin, and post-modification inspections and applicable corrective actions (repairs of cracking). Compliance times for on-condition actions depend on inspection type, inspection findings, and modification status. Initial compliance times for post-modification inspections range from within 10,000 flight cycles or 50,000 flight hours, whichever occurs first after the modification; and within 30,000 flight cycles, 90,000 flight hours, or before the result of a certain total flight cycle and total flight hour equation, whichever occurs first after the modification. The repetitive intervals range from 8,000 flight cycles or 25,000 flight hours, whichever occurs first, to 11,000 flight cycles or 56,000 flight hours, whichever occurs first. Repairs of cracking found during post-modification inspections are to be accomplished before further flight.

The FAA also reviewed Boeing Multi Operator Message MOM-MOM-24-0054-01B, dated January 26, 2024. This service information specifies corrections for Boeing Alert Requirements Bulletin 777-57A0122 RB, dated October 8, 2021, that address a non-destructive test manual (NDTM) error, fastener callout errors, inadequate cap seal instructions, figure orientation errors, minimum gap errors, missing fasteners on certain figures, affected groups missing from certain figures, and typographical errors.

This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in ADDRESSES .

Proposed AD Requirements in This NPRM

This proposed AD would require accomplishing the actions specified in the service information already described and except for any differences identified as exceptions in the regulatory text of this proposed AD. For information on the procedures and compliance times, see this service information at regulations.gov under Docket No. FAA-2024-0769.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 272 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:

Estimated Costs

Action	Labor cost	Parts cost	Cost per product	Cost on U.S. operators
External or internal inspections	Up to 21 work-hours × $85 per hour = $1,785 per inspection cycle	$0	$1,785 per inspection cycle	$485,520 per inspection cycle.

The FAA estimates the following costs to do any necessary on-condition actions 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 actions:

On-Condition Costs

Action	Labor cost	Parts cost	Cost per product
Modification	420 work-hours × $85 per hour = $35,700	$40,620	$76,320.
Post-modification inspections	46 work-hours × $85 per hour = $3,910 per inspection cycle	0	3,910 per inspection cycle.

The FAA has received no definitive data on which to base the cost estimates for the on-condition repairs specified in this proposed AD.

The FAA has included all known costs in its cost estimate. According to the manufacturer, however, some or all of the costs of this proposed 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

The FAA determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would 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 this proposed regulation:

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

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

(3) Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Incorporation by reference
• Safety

The Proposed Amendment

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

PART 39—AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

§ 39.13

[Amended]

2. The FAA amends § 39.13 by adding the following new airworthiness directive:

The Boeing Company: Docket No. FAA-2024-0769; Project Identifier AD-2023-00556-T.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by May 13, 2024.

(b) Affected ADs

This AD affects AD 2023-17-14, Amendment 39-22541 (88 FR 60111, August 31, 2023) (AD 2023-17-14).

(c) Applicability

This AD applies to The Boeing Company Model 777-200, -200LR, -300, -300ER, and 777F series airplanes, certificated in any category, as identified in Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023.

(d) Subject

Air Transport Association (ATA) of America Code 53, Fuselage.

(e) Unsafe Condition

This AD was prompted by a report indicating multiple findings of cracks in the fuselage skin common to the underwing longeron (UWL). The FAA is issuing this AD to address fuselage skin cracking caused by cold work surface upset that is not removed from the mating parts and high joint load transfer or significant local bending stresses at critical fastener locations. The unsafe condition, if not addressed, could result in an inability of a principal structural element (PSE) to sustain limit load, leading to reduced structural integrity of the airplane and possible loss of control of the airplane.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Required Actions

Except as specified by paragraph (h) of this AD: At the applicable times specified in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, do all applicable actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023.

Note 1 to paragraph (g): Guidance for accomplishing the actions required by this AD can be found in Boeing Alert Service Bulletin 777-53A0100, dated March 16, 2023, which is referred to in Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023.

Note 2 to paragraph (g): Guidance for accomplishing certain on-condition actions required by paragraph (g) of this AD can be found Boeing Service Bulletin 777-53-0084 Revision 2, dated December 9, 2020; Boeing Service Bulletin 777-53-0087 Revision 1, dated March 4, 2020; and Boeing Alert Requirements Bulletin 777-57A0122 RB, dated October 8, 2021.

(h) Exceptions to Service Information Specifications

(1) Where the Compliance Time columns of the tables in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, use the phrase “the original issue date of Requirements Bulletin 777-53A0100 RB,” this AD requires using the effective date of this AD.

(2) Where Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, and any service information referenced in Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, specifies contacting Boeing for repair instructions: This AD requires doing the repair using a method approved in accordance with the procedures specified in paragraph (j) of this AD.

(3) Where any service information referenced in Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, specifies applying a cap seal (sealant) to a fastener, fastener head, and fastener threads and collars, for this AD, during application of any cap seal to a fastener, fastener head, or fastener threads and collars, the cap seal must be applied using a cap sealing procedure with thickness greater than or equal to the dimensions given in Figure 1 to paragraph (h)(3) of this AD.

Figure 1 to Paragraph (h)(3)—Cap Sealing Dimensions (all Dimensions are in Inches)

(4) Where Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, specifies doing actions “in accordance with Revision 2 of Boeing Service Bulletin 777-53-0084,” for this AD, where flagnote (f) of Figure 7 and Figure 22 of that referenced service information (“Revision 2 of Boeing Service Bulletin 777-53-0084”) includes a sealant callout of Boeing Material Specification (BMS) 5-45 or an optional BMS 5-95, only BMS 5-45 is allowed.

(5) Where Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, specifies doing actions “in accordance with Revision 1 of Boeing Service Bulletin 777-53-0087,” for this AD, where flagnote (f) of Figure 13 and Figure 49 of that referenced service information (“Revision 1 of Boeing Service Bulletin 777-53-0087”) includes a sealant callout of BMS 5-45 or an optional BMS 5-95, only BMS 5-45 is allowed.

(6) Where Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023, specifies doing actions “in accordance with the original issue of Boeing Alert Requirements Bulletin 777-57A0122 RB,” for this AD, the exceptions specified in paragraph (h)(6)(i) through (v) of this AD apply to that referenced service information (“the original issue of Boeing Alert Requirements Bulletin 777-57A0122 RB”) and the corrections identified in Boeing Multi Operator Message MOM-MOM-24-0054-01B, dated January 26, 2024, apply to that referenced service information.

(i) Where the “Compliance” paragraph of the referenced service information identifies “Tables 1 through 50,” the correct number of tables is Tables 1 through 54.

(ii) The referenced service information does not specify the application of cap seals to underwing longeron fasteners, fastener heads, and fastener threads and collars for the airplane groups and configurations identified in paragraphs (h)(6)(ii)(A) through (D) of this AD. For those airplane groups and configurations, the application of a cap seal to the underwing longeron fasteners at the locations identified in Figures 81 and 144 is required during installation of the underwing longeron and must be applied using a cap sealing procedure with thickness greater than or equal to the dimensions given in Figure 1 to paragraph (h)(3) of this AD.

(A) Groups 7 and 8, Configurations 5 through 8, on the left side.

(B) Group 9, Configurations 1 and 2, on the left side.

(C) Groups 7 and 8, Configurations 2, 6, 10, and 14, on the right side.

(D) Group 9, Configurations 1 and 3, on the right side.

(iii) For any inspection that may require the removal of fastener cap seals, if the cap seal is removed, a cap seal of BMS 5-45 sealant must be reapplied using a cap sealing procedure with a thickness equal to or greater than the dimensions specified in Figure 1 to paragraph (h)(3) of this AD before further flight after completion of the inspection.

(iv) The referenced service information does not require the restoration of any sealant removed to accomplish high frequency eddy current and ultrasonic inspections external to the fuel tank in Figures 1, 7, 11, and 17. Following completion of any inspection required by those figures, replacement of the sealant described in paragraph (h)(6)(iv)(A) and repair of the sealant described in paragraph (h)(6)(iv)(B) of this AD, as applicable, is required.

(A) Where any sealant was removed from the heads of fasteners, before further flight, cover and fillet seal the fasteners using BMS 5-45 or BMS 5-95 sealant.

Note 3 to paragraph (h)(6)(iv)(A): Guidance for accomplishing the actions required by paragraph (h)(6)(iv)(A) of this AD can be found in the Boeing Standard Overhaul Practices Manual (SOPM) section 20-50-19.

(B) Following any sealant replacement required by paragraph (h)(6)(iv)(A) of this AD, where any secondary fuel barrier coating was removed, before further flight, repair the secondary fuel barrier using BMS 5-81 sealant.

Note 4 to paragraph (h)(6)(iv)(B): Guidance for accomplishing the actions required by paragraph (h)(6)(iv)(B) of this AD can be found in Boeing Model 777 Aircraft Maintenance Manual (AMM) section 28-11-00.

(v) The Effectivity of the referenced service information does not include Boeing Model 777F series airplanes having line numbers 1713, 1717, 1720, and 1724 through 1742 inclusive. For those airplanes the applicable actions for Group 6 must be done.

(i) Terminating Action for AD 2023-17-14

For airplanes on which a front spar lower chord modification specified in Boeing Alert Requirements Bulletin 777-57A0122 RB is done as part of the requirements of paragraphs (g) and (h)(6) of this AD, the modification requirements of paragraph (g) of AD 2023-17-14 are terminated for the applicable side (left or right) on which the modification was done.

(j) Alternative Methods of Compliance (AMOCs)

(1) The Manager, AIR-520, Continued Operational Safety Branch, FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or responsible Flight Standards Office, as appropriate. If sending information directly to the manager of the Continued Operational Safety Branch, send it to the attention of the person identified in paragraph (k)(1) of this AD. Information may be emailed to: [e-mail].

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the responsible Flight Standards Office.

(3) An AMOC that provides an acceptable level of safety may be used for any repair, modification, or alteration required by this AD if it is approved by The Boeing Company Organization Designation Authorization (ODA) that has been authorized by the Manager, AIR-520, Continued Operational Safety Branch, FAA, to make those findings. To be approved, the repair method, modification deviation, or alteration deviation must meet the certification basis of the airplane, and the approval must specifically refer to this AD.

(k) Related Information

(1) For more information about this AD, contact Luis Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail].

(2) Service information identified in this AD that is not incorporated by reference is available at the addresses specified in paragraph (l)(3) of this AD.

(l) Material Incorporated by Reference

(1) The Director of the Federal Register approved the incorporation by reference (IBR) of the service information listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use this service information as applicable to do the actions required by this AD, unless the AD specifies otherwise.

(i) Boeing Alert Requirements Bulletin 777-53A0100 RB, dated March 16, 2023.

(ii) Boeing Multi Operator Message MOM-MOM-24-0054-01B, dated January 26, 2024.

(3) For service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone [phone]; website myboeingfleet.com.

(4) 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.

(5) You may view this material at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, visit www.archives.gov/​federal-register/​cfr/​ibr-locations or email [e-mail].

Issued on March 22, 2024.

Victor Wicklund,

Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.