2023-11199. 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 737–600, 737–700, and 737–800 series airplanes. This proposed AD was prompted by an evaluation by the design approval holder (DAH) indicating the fuselage skin at the double row of fasteners centered on certain stringers is subject to skin cracking. This proposed AD is intended to complete certain programs to support the airplane reaching its limit of validity (LOV). This proposed AD would require repetitive inspections for cracks of skin repairs at Stringer S–17, and corrective actions if necessary. 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 July 10, 2023.

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–2023–1041; 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–2023–1041.

FOR FURTHER INFORMATION CONTACT:

Bill Ashforth, Senior Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 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–2023–1041; Project Identifier AD–2022–01223–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 Bill Ashforth, Senior Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 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

As described in FAA Advisory Circular 120–104 ( http://www.faa.gov/​documentLibrary/​media/​Advisory_​Circular/​120-104.pdf), several programs have been developed to support initiatives that will ensure the continued airworthiness of aging airplane structure. The last element of those initiatives is the requirement to establish an LOV of the engineering data that support the structural maintenance program under 14 CFR 26.21. This proposed AD is the result of an assessment of the previously established programs by the DAH during the process of establishing the LOV for the affected airplanes. The actions specified in this proposed AD are necessary to complete certain programs to ensure the continued airworthiness of aging airplane structure and to support an airplane reaching its LOV.

The FAA has received a report indicating the fuselage skin at the double row of fasteners centered on stringers S–17L and S–17R, at station (STA) 360 to STA 380 and at STA 888 to STA 907 is subject to skin cracking. During airplane production, a structural preload was created in the body skin during installation of S–17 stringers. Analysis by Boeing shows that this preload, combined with pressure cycles, can cause cracks in the skin prior to reaching the design service objective (DSO). For Model 737–600, 737–700, and 737–800 series airplanes after Line Number 269, the sequence of assembly was changed to eliminate the preload.

Boeing issued Service Bulletin 737–53A1217, dated August 9, 2001, to specify repetitive inspections of the skin for cracking; however, that service information was not required by an AD because existing maintenance planning document (MPD) inspections were determined to be adequate to address skin cracking. Several airplanes have had inspections and/or repairs accomplished at STA 360 to STA 380. The FAA and Boeing have since determined that certain existing post-repair inspections are inadequate to address the unsafe condition. The actions in paragraph (g) of this proposed AD would therefore apply only to airplanes on which a repair has been done as specified in Boeing Alert Service Bulletin 737–53A1217 (identified as Group 1 through 3, Configuration 3 in Boeing Alert Service Bulletin 737–53A1217). Once a certain repair is accomplished on an airplane, post-repair inspections must be accomplished on that airplane, as specified in this proposed AD. This proposed AD would require only the post-repair inspections and corrective actions specified in Tables 3 through 6 of Boeing Alert Service Bulletin 737–53A1217. Airplanes identified as Group 1 through 3, Configurations 1 and 2 in Boeing Alert Service Bulletin 737–53A1217 become Configuration 3 airplanes after accomplishing a repair specified in Boeing Alert Service Bulletin 737–53A1217. This unsafe condition, if not addressed, could result in an undetected crack that could grow to critical length, and result in possible rapid decompression and loss of structural integrity of the airplane.

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 Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022. This service information specifies procedures for, among other actions, repetitive internal and external detailed inspections, low frequency eddy current (LFEC), and medium frequency eddy current (MFEC) inspections for cracks of the skin repair of S–17, STA 360 to STA 380 and STA 888 to STA 907, left and right sides of the airplane. Corrective actions include repair.

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 identified as “RC” (required for compliance) in the Accomplishment Instructions of Boeing Alert Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022, already described, 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–2023–1041.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 106 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 Post Repair Inspection	56 work-hours × $85 per hour = $4,760 per inspection cycle	0	$4,760 per inspection cycle	$504,560 per inspection cycle.
Internal Post Repair Inspections	52 work-hours × $85 per hour = $4,420 per inspection cycle	0	$4,420 per inspection cycle	$468,520 per inspection cycle.

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

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–2023–1041; Project Identifier AD–2022–01223–T.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by July 10, 2023.

(b) Affected ADs

None.

(c) Applicability

This AD applies to The Boeing Company Model 737–600, 737–700, and 737–800 series airplanes, certificated in any category, as identified in Boeing Alert Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022.

(d) Subject

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

(e) Unsafe Condition

This AD was prompted by an evaluation by the design approval holder (DAH) indicating the fuselage skin at the double row of fasteners centered on certain stringers is subject to skin cracking. The FAA is issuing this AD to address fatigue cracks at certain fasteners centered on Stringers S–17L and S–17R, at station (STA) 360 to STA 380 and at STA 888 to STA 907. Such undetected fatigue cracks, if not addressed, could grow to a critical length, which could result in rapid decompression and loss of structural integrity of the airplane.

(f) Compliance

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

(g) Required Actions

For Group 1 through 3, Configuration 3 airplanes as identified in Boeing Alert Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022: Except as specified in paragraph (h) of this AD, at the applicable times specified in Tables 3 through 6 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022, do all applicable actions identified as “RC” (required for compliance) in, and in accordance with, the Accomplishment Instructions of Boeing Alert Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022.

(h) Exceptions to Service Information Specifications

Where Boeing Alert Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022, specifies contacting Boeing for repair instructions or for alternative inspections: This AD requires doing the repair, or doing the alternative inspections and applicable on-condition actions, using a method approved in accordance with the procedures specified in paragraph (i) of this AD.

(i) 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 certification office, send it to the attention of the person identified in paragraph (k) 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, Seattle ACO 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.

(4) Except as specified by paragraph (h) of this AD: For service information that contains steps that are labeled as Required for Compliance (RC), the provisions of paragraphs (i)(4)(i) and (ii) of this AD apply.

(i) The steps labeled as RC, including substeps under an RC step and any figures identified in an RC step, must be done to comply with the AD. If a step or substep is labeled “RC Exempt,” then the RC requirement is removed from that step or substep. An AMOC is required for any deviations to RC steps, including substeps and identified figures.

(ii) Steps not labeled as RC may be deviated from using accepted methods in accordance with the operator's maintenance or inspection program without obtaining approval of an AMOC, provided the RC steps, including substeps and identified figures, can still be done as specified, and the airplane can be put back in an airworthy condition.

(j) Related Information

For more information about this AD, contact Bill Ashforth, Senior Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail].

(k) 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 Service Bulletin 737–53A1217, Revision 1, dated September 8, 2022.

(ii) [Reserved]

(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 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.

(5) You may view this service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, [e-mail], or go to: www.archives.gov/​federal-register/​cfr/​ibr-locations.html.

Issued on May 9, 2023.

Michael Linegang,

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