Proposed Rule

Airworthiness Directives; The Boeing Company Airplanes

A Proposed Rule by the Federal Aviation Administration on 03/30/2026

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• Public Inspection Published Document: 2026-06067 (91 FR 15566) Document Headings ###### Department of Transportation

Federal Aviation Administration

1. 14 CFR Part 39
2. [Docket No. FAA-2026-2726; Project Identifier AD-2025-00364-T]
3. RIN 2120-AA64

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 indicating that adjusting the upper locking hydraulic actuator proximity sensor targets in accordance with certain data in the aircraft maintenance manual (AMM) could result in incorrect upper locking hydraulic actuator indications, which could result in a thrust reverser that indicates `locked' when it is not locked. This proposed AD would require conducting measurements, tests, and operational checks of the upper locking hydraulic actuator for certain functions, performing applicable on-condition actions, and revising the existing maintenance or inspection program, as applicable, to incorporate certain certification maintenance requirements (CMR). The FAA is proposing this AD ( printed page 15567) to address the unsafe condition on these products.

DATES:

The FAA must receive comments on this proposed AD by May 14, 2026.

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.
• 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-2026-2726; 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 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-2026-2726.

FOR FURTHER INFORMATION CONTACT:

Erica Bayles, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 907-271-5844; email: erica.e.bayles@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 using a method listed under the ADDRESSES section. Include “Docket No. FAA-2026-2726; Project Identifier AD-2025-00364-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 Erica Bayles, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 907-271-5844; email: erica.e.bayles@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 indicating that adjusting the upper locking hydraulic actuator proximity sensor targets in accordance with certain data in the AMM could result in incorrect upper locking hydraulic actuator indications, which could result in a thrust reverser that indicates `locked' when it is not locked. This condition, if not addressed, could lead to a decrease in safety margins to prevent a possible uncommanded in-flight deployment of the thrust reverser, which could result in loss of control 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.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-78A1099 RB, dated July 8, 2025. This material specifies procedures for the following checks to verify the lock indication function of each upper locking hydraulic actuator of the left and right thrust reverser halves of each engine position and applicable on-condition actions:

• Measurement of manual unlock handle assembly angular free-play.
• Lock integrity test of the upper locking hydraulic actuator.
• Operational check of the manual unlock handle assembly torsion spring.
• Measurement of the clearance between the upper locking hydraulic actuator proximity sensor and proximity sensor target leading edge.
• Measurement of the upper locking hydraulic actuator proximity sensor target. On-condition actions include replacing the upper locking hydraulic actuator manual unlock handle assembly torsion spring, replacing the upper locking hydraulic actuator proximity sensor target, deactivating the thrust reverser for flight, and replacing the actuator.

This material also specifies procedures for revising the operator's maintenance program to incorporate certain inspections and checks of the engine thrust reverser (CMR items 70-CMR-01 and 78-CMR-01 through 78-CMR-07 of Boeing 737-600/700/700C/800/900/900ER CMR D626A001-9-03, dated September 2023).

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 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-2026-2726.

Terminating Action for Related Rulemaking

The FAA issued AD 2019-18-03, Amendment 39-19730 (84 FR 49005, September 18, 2019) (AD 2019-18-03), for all The Boeing Company Model 737 series airplanes, certificated in any category, excluding Model 737-100, ( printed page 15568) -200, -200C, -300, -400, and -500 series airplanes. AD 2019-18-03 was prompted by a report indicating that alteration of thrust reverser upper locking actuators in accordance with certain data contained in the Boeing AMM could delay or prevent detection of the failure of the locking mechanism of a thrust reverser upper locking actuator. AD 2019-18-03 requires revising the existing maintenance or inspection program to remove certain text that instructs the maintainers to remove material from or grind or trim the sensor target of the thrust reverser upper locking actuator. For Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes, AD 2019-18-03 also requires repetitive integrity tests of the thrust reverser upper locking actuator.

The FAA has determined that accomplishing the actions required by paragraph (g) of this proposed AD would terminate the actuator integrity test and corrective actions required by paragraphs (i), (j), and (k) of AD 2019-18-03.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 1,805 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 |
| --- | --- | --- | --- | --- |
| Measurements, integrity test, and operational check | 18 work-hours × $85 per hour = $1,530 | $0 | $1,530 | $2,761,650 |
The FAA has determined that revising the maintenance or inspection program takes an average of 90 work-hours per operator, although the agency recognizes that this number may vary from operator to operator. Since operators incorporate maintenance or inspection program changes for their affected fleet(s), the FAA has determined that a per-operator estimate is more accurate than a per-airplane estimate. Therefore, the FAA estimates the average total cost per operator to be $7,650 (90 work-hours × $85 per work-hour).

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:

| Action | Labor cost | Parts cost | Cost per product |
| --- | --- | --- | --- |
| Actuator replacement | 8 work-hours × $85 per hour = $680 | $47,240 | $47,920. |
| Torsion spring replacement | 1 work-hour × $85 per hour = $85 | $19 | $104. |
| Proximity sensor target replacement | 1 work-hour × $85 per hour = $85 | Up to $130 | Up to $215. |

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-2026-2726; Project Identifier AD-2025-00364-T.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by May 14, 2026. ( printed page 15569)

(b) Affected ADs

This AD affects AD 2019-18-03, Amendment 39-19730 (84 FR 49005, September 18, 2019) (AD 2019-18-03).

(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 78, Thrust Reverser.

(e) Unsafe Condition

This AD was prompted by a report indicating that adjusting the upper locking hydraulic actuator proximity sensor targets in accordance with certain data in the aircraft maintenance manual (AMM) could result in incorrect upper locking hydraulic actuator indications, which could result in a thrust reverser that indicates `locked' when it is not locked. The FAA is issuing this AD to address this condition which, if not addressed, could lead to a decrease in safety margins to prevent a possible uncommanded in-flight deployment of the thrust reverser, which could result in 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 737-78A1099 RB, dated July 8, 2025, do all applicable actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-78A1099 RB, dated July 8, 2025.

Note 1 to paragraph (g): Guidance for accomplishing the actions required by this AD can be found in Boeing Alert Service Bulletin 737-78A1099, dated July 8, 2025, which is referred to in Boeing Alert Requirements Bulletin 737-78A1099 RB, dated July 8, 2025.

(h) Exceptions to Requirements Bulletin Specifications

(1) Where the Compliance Time column of the tables in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 737-78A1099 RB, dated July 8, 2025, refers to the original issue date of Requirements Bulletin 737-78A1099 RB, this AD requires using the effective date of this AD.

(2) Where note (a) of table 12 of the Compliance paragraph of Boeing Alert Requirements Bulletin 737-78A1099 RB, dated July 8, 2025, specifies “Boeing recommends operators accomplish the initial inspection required by 78-CMR-07 prior to completing this RB on airplanes with more than 28,000 flight hours. The initial compliance time for accomplishing 78-CMR-07 is prior to the accumulation of 28,000 total flight hours”, this AD requires replacing that text with “The initial compliance time for accomplishing the initial inspection required by 78-CMR-07 is before further flight after accomplishing any procedure specified in Table 1 or prior to the accumulation of 28,000 total flight hours, whichever occurs later”.

(i) No Alternative Actions or Intervals

After the existing maintenance or inspection program has been revised as required by paragraph (g) of this AD, no alternative actions (e.g., inspections) or intervals may be used unless the actions and intervals are approved as an alternative method of compliance in accordance with the procedures specified in paragraph (k) of this AD.

(j) Terminating Action for Certain Requirements of AD 2019-18-03

Accomplishing the actions required by paragraph (g) of this AD terminates the actuator integrity test and corrective actions required by paragraphs (i), (j), and (k) of AD 2019-18-03.

(k) 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 (l)(1) of this AD. Information may be emailed to: AMOC@faa.gov. Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the responsible Flight Standards Office.

(2) 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.

(l) Additional Information

(1) For more information about this AD, contact Erica Bayles, Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 907-271-5844; email: erica.e.bayles@faa.gov.

(2) Material identified in this AD that is not incorporated by reference is available at the address specified in paragraph (m)(3) of this AD.

(m) 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 737-78A1099 RB, dated July 8, 2025.

(ii) [Reserved].

(3) For 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 24, 2026.

Lona C. Saccomando,

Acting Deputy Director, Integrated Certificate Management Division, Aircraft Certification Service.

[FR Doc. 2026-06067 Filed 3-27-26; 8:45 am]

BILLING CODE 4910-13-P

Published Document: 2026-06067 (91 FR 15566)