90 FR 71 pgs. 15662-15664 - Airworthiness Directives; The Boeing Company Airplanes
Type: PRORULEVolume: 90Number: 71Pages: 15662 - 15664
Pages: 15662, 15663, 15664Docket number: [Docket No. FAA-2025-0469; Project Identifier AD-2024-00640-T]
FR document: [FR Doc. 2025-06274 Filed 4-14-25; 8:45 am]
Agency: Transportation Department
Sub Agency: Federal Aviation Administration
Official PDF Version: PDF Version
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2025-0469; Project Identifier AD-2024-00640-T]
RIN 2120-AA64
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 all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. This proposed AD was prompted by a report of under-torqued and missing nuts on the horizontal stabilizer trim actuator (HSTA) lower gimbal assembly. This proposed AD would require a review of maintenance records to determine if an overhauled HSTA was inspected and corrective actions were accomplished using certain service information, 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 30, 2025.
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: 202-493-2251.
• Fax: 202-493-2251.
• 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-2025-0469; 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 the Boeing material identified in this proposed AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone 562-797-1717; website myboeingfleet.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 at regulations.gov under Docket No. FAA-2025-0469.
FOR FURTHER INFORMATION CONTACT:
Luis Cortez-Muniz, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 206-231-3958; email: luis.a.cortez-muniz@faa.gov.
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 the ADDRESSES section. Include "Docket No. FAA-2025-0469; Project Identifier AD-2024-00640-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: 206-231-3958; email: luis.a.cortez-muniz@faa.gov. 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 a report of under-torqued and missing nuts on the HSTA lower gimbal assembly during a routine lubrication of the HSTA. The yoke assembly was found separated from the fork assembly at one corner but was still engaged on the related trunnion on the HSTA. Loss of the HSTA primary load path can result in limit cycle oscillation (LCO). LCO may be detectable by flight crew through airframe vibration or pitch oscillations but could go undetected for many fight cycles. Incorrectly installed nuts on the HSTA lower gimbal assembly, if not addressed, could result in a HSTA lower gimbal assembly disconnect resulting in loss of load path redundancy preventing continued safe flight and landing.
FAA's Determination
[top] 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.
Material Incorporated by Reference Under 1 CFR Part 51
The FAA reviewed Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024. This material specifies procedures for a review of maintenance records to determine if an overhauled HSTA was inspected and corrective actions were accomplished using certain service information. On-condition actions include general visual inspections, torque value measurements, replacement of under-torqued nuts, HSTA replacement, and repair of cracking and corrosion.
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.
Proposed AD Requirements in This NPRM
This proposed AD would require accomplishing the actions specified in the material already described, except as discussed under "Differences Between this Proposed AD and the Referenced Material," 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 material at regulations.gov under Docket No. FAA-2025-0469.
Differences Between This Proposed AD and the Referenced Material
The effectivity of Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024, is limited to Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes, having certain line numbers. However, the applicability of this proposed AD includes all Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes. Because the affected parts are rotable parts, the FAA has determined that these parts could later be installed on airplanes that were initially delivered with acceptable parts, thereby subjecting those airplanes to the unsafe condition.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would affect 2,060 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:
| Action | Labor cost | Parts cost | Cost per product | Cost on U.S. operators |
|---|---|---|---|---|
| Records review | 1 work-hour × $85 per hour = $85 | $0 | $85 | $175,100 |
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 this replacement:
| Action | Labor cost | Parts cost | Cost per product |
|---|---|---|---|
| General visual inspections and torque value measurements | Up to 5 work-hours × $85 per hour = $425 | $0 | Up to $425. |
| Replacement of under-torqued nuts | Up to 2 work-hours × $85 per hour = $170 | Negligible | Up to $170. |
| Replacement of HSTA | 3 work-hours × $85 per hour = $255 | $325,585 | $325,840. |
The FAA has received no definitive data on which to base the cost estimates for the on-condition 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:
[top] The Boeing Company: Docket No. FAA-2025-0469; Project Identifier AD-2024-00640-T.
(a) Comments Due Date
The FAA must receive comments on this airworthiness directive (AD) by May 30, 2025.
(b) Affected ADs
None.
(c) Applicability
This AD applies to all The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes, certificated in any category.
(d) Subject
Air Transport Association (ATA) of America Code 27, Flight controls.
(e) Unsafe Condition
This AD was prompted by a report of under-torqued and missing nuts on the horizontal stabilizer trim actuator (HSTA) lower gimbal assembly. The FAA is issuing this AD to address incorrectly installed nuts on the HSTA lower gimbal assembly. The unsafe condition, if not addressed, could result in a HSTA lower gimbal assembly disconnect resulting in loss of load path redundancy preventing continued safe flight and landing.
(f) Compliance
Comply with this AD within the compliance times specified, unless already done.
(g) Required Actions
For airplanes with an overhauled HSTA installed using a procedure other than 737-600/-700/-800/-900 Aircraft Maintenance Manual (AMM) 27-41-81 dated January 6, 2024, or later: Except as specified by paragraph (h) of this AD, at the applicable times specified in the "Compliance" paragraph of Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024, do all applicable actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024.
Note 1 to paragraph (g):
Guidance for accomplishing the actions required by this AD can be found in Boeing Alert Service Bulletin 737-27A1330, dated October 7, 2024, which is referred to in Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024.
(h) Exceptions to Requirements Bulletin Specifications
(1) Where the Compliance Time columns of the tables in the "Compliance" paragraph of Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024, refer to the original issue date of Requirements Bulletin 737-27A1330 RB, this AD requires using the effective date of this AD.
(2) Where Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024, 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.
(i) Parts Installation Prohibition
As of the effective date of this AD, no person may use 737-600/-700/-800/-900 AMM 27-41-81 dated earlier than January 6, 2024, to install an overhauled HSTA on any airplane.
(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 certification office, send it to the attention of the person identified in paragraph (k)(1) of this AD. Information may be emailed to: AMOC@faa.gov.
(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: 206-231-3958; email: luis.a.cortez-muniz@faa.gov.
(2) Material identified in this AD that is not incorporated by reference is available at the address specified in paragraph (l)(3) this AD.
(l) Material Incorporated by Reference
(1) The Director of the Federal Register approved the incorporation by reference of the material listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
(2) You must use this material as applicable to do the actions required by this AD, unless the AD specifies otherwise.
(i) Boeing Alert Requirements Bulletin 737-27A1330 RB, dated October 7, 2024.
(ii) [Reserved]
(3) For the Boeing material 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 562-797-1717; 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 fr.inspection@nara.gov.
Issued on March 17, 2025.
Victor Wicklund,
Deputy Director, Integrated Certificate Management Division, Aircraft Certification Service.
[FR Doc. 2025-06274 Filed 4-14-25; 8:45 am]
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