Proposed Rule2026-06067
Airworthiness Directives; The Boeing Company Airplanes
Primary source
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Published
March 30, 2026
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
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 to address the unsafe condition on these products.
Full Text
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<title>Federal Register, Volume 91 Issue 60 (Monday, March 30, 2026)</title>
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[Federal Register Volume 91, Number 60 (Monday, March 30, 2026)]
[Proposed Rules]
[Pages 15566-15569]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-06067]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2026-2726; Project Identifier AD-2025-00364-T]
RIN 2120-AA64
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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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
[[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:
<bullet> Federal eRulemaking Portal: Go to <a href="http://regulations.gov">regulations.gov</a>. Follow
the instructions for submitting comments.
<bullet> Fax: 202-493-2251.
<bullet> 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.
<bullet> 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 <a href="http://regulations.gov">regulations.gov</a> 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:
<bullet> 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 <a href="http://myboeingfleet.com">myboeingfleet.com</a>.
<bullet> 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 <a href="http://regulations.gov">regulations.gov</a> 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: <a href="/cdn-cgi/l/email-protection#d1b4a3b8b2b0ffb4ffb3b0a8bdb4a291b7b0b0ffb6bea7"><span class="__cf_email__" data-cfemail="82e7f0ebe1e3ace7ace0e3fbeee7f1c2e4e3e3ace5edf4">[email protected]</span></a>.
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
<a href="http://regulations.gov">regulations.gov</a>, 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: <a href="/cdn-cgi/l/email-protection#bfdacdd6dcde91da91dddec6d3daccffd9dede91d8d0c9"><span class="__cf_email__" data-cfemail="8ce9fee5efeda2e9a2eeedf5e0e9ffcceaededa2ebe3fa">[email protected]</span></a>.
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:
<bullet> Measurement of manual unlock handle assembly angular free-
play.
<bullet> Lock integrity test of the upper locking hydraulic
actuator.
<bullet> Operational check of the manual unlock handle assembly
torsion spring.
<bullet> Measurement of the clearance between the upper locking
hydraulic actuator proximity sensor and proximity sensor target leading
edge.
<bullet> 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 <a href="http://regulations.gov">regulations.gov</a> 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,
[[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:
Estimated Costs
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Cost per Cost on U.S.
Action Labor cost Parts cost product operators
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Measurements, integrity test, and 18 work-hours x $85 per $0 $1,530 $2,761,650
operational check. hour = $1,530.
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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 x $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:
On-Condition Costs
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Action Labor cost Parts cost Cost per product
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Actuator replacement................. 8 work-hours x $85 per $47,240................ $47,920.
hour = $680.
Torsion spring replacement........... 1 work-hour x $85 per $19.................... $104.
hour = $85.
Proximity sensor target replacement.. 1 work-hour x $85 per Up to $130............. Up to $215.
hour = $85.
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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
0
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
0
2. The FAA amends Sec. 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.
[[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:
<a href="/cdn-cgi/l/email-protection#286965676b684e4949064f475e"><span class="__cf_email__" data-cfemail="480905070b082e2929662f273e">[email protected]</span></a>. 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: <a href="/cdn-cgi/l/email-protection#dfbaadb6bcbef1baf1bdbea6b3baac9fb9bebef1b8b0a9"><span class="__cf_email__" data-cfemail="1376617a70723d763d71726a7f7660537572723d747c65">[email protected]</span></a>.
(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 <a href="http://myboeingfleet.com">myboeingfleet.com</a>.
(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 <a href="http://www.archives.gov/federal-register/cfr/ibr-locations">www.archives.gov/federal-register/cfr/ibr-locations</a> or email <a href="/cdn-cgi/l/email-protection#076175296e6974776264736e6869476966756629606871"><span class="__cf_email__" data-cfemail="1c7a6e3275726f6c797f687573725c727d6e7d327b736a">[email protected]</span></a>.
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
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