Proposed Rule2026-19360
Airworthiness Directives; Airbus SAS Airplanes
Primary source
Metadata and text below are from the Federal Register, a public-domain U.S. government work. Always verify the official published version before relying on it for any legal matter.
Published
September 22, 2026
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
The FAA proposes to adopt a new airworthiness directive (AD) for certain Airbus SAS Model A350-941 airplanes. This proposed AD was prompted by reports of engine health monitoring (EHM) messages requiring premature removal of hydro-mechanical units (HMUs). This proposed AD would require replacing certain HMUs before reaching a reduced life limit and would limit the installation of affected parts under certain conditions. 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 182 (Tuesday, September 22, 2026)</title>
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[Federal Register Volume 91, Number 182 (Tuesday, September 22, 2026)]
[Proposed Rules]
[Pages 60033-60035]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-19360]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2026-8807; Project Identifier MCAI-2025-01385-T]
RIN 2120-AA64
Airworthiness Directives; Airbus SAS 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 certain Airbus SAS Model A350-941 airplanes. This proposed AD was
prompted by reports of engine health monitoring (EHM) messages
requiring premature removal of hydro-mechanical units (HMUs). This
proposed AD would require replacing certain HMUs before reaching a
reduced life limit and would limit the installation of affected parts
under certain conditions. 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 November 6,
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-2026-8807; 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, the mandatory continuing airworthiness
information (MCAI), any comments received, and other information. The
street address for Docket Operations is listed above.
Material Incorporated by Reference:
<bullet> For European Union Aviation Safety Agency (EASA) material
identified in this proposed AD, contact EASA, Konrad-Adenauer-Ufer 3,
50668 Cologne, Germany; telephone +49 221 8999 000; email
<a href="/cdn-cgi/l/email-protection#8ccdc8ffcce9edffeda2e9f9fee3fceda2e9f9"><span class="__cf_email__" data-cfemail="f9b8bd8ab99c988a98d79c8c8b968998d79c8c">[email protected]</span></a>. You may find this material on the EASA website at
ad.easa.europa.eu. It is also available at <a href="http://regulations.gov">regulations.gov</a>under Docket
No. FAA-2026-8807.
<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.
FOR FURTHER INFORMATION CONTACT: Anthony Decaro, Aviation Safety
Engineer, FAA, 2200 South 216th St., Des Moines, WA 98198; phone: 562-
627-5374; email: <a href="/cdn-cgi/l/email-protection#bedfd0cad6d1d0c790da90dadbdddfccd1fed8dfdf90d9d1c8"><span class="__cf_email__" data-cfemail="abcac5dfc3c4c5d285cf85cfcec8cad9c4ebcdcaca85ccc4dd">[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-2026-8807;
Project Identifier MCAI-2025-01385-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
[[Page 60034]]
should be sent to Anthony Decaro, Aviation Safety Engineer, FAA, 2200
South 216th St., Des Moines, WA 98198; phone: 562-627-5374; email:
<a href="/cdn-cgi/l/email-protection#f79699839f98998ed993d9939294968598b7919696d9909881"><span class="__cf_email__" data-cfemail="dabbb4aeb2b5b4a3f4bef4bebfb9bba8b59abcbbbbf4bdb5ac">[email protected]</span></a>. Any commentary that the FAA receives which is
not specifically designated as CBI will be placed in the public docket
for this rulemaking.
Background
EASA, which is the Technical Agent for the Member States of the
European Union, has issued EASA AD 2025-0183, dated August 25, 2025
(EASA AD 2025-0183) (also referred to as the MCAI), to correct an
unsafe condition for Airbus SAS Model A350-941 airplanes equipped with
Rolls-Royce Trent XWB-84 engines, Trent XWB-84EP engines, or Trent XWB-
75 engines. The MCAI states that the EHM identified abnormal HMU
behavior via ``Fuel Metering Valve position high'' alerts, requiring
premature removal of HMUs. Root cause analysis traced the issue to
wear-induced stiction within the combining spill valve (CSV), where
piston-to-housing friction prevented full closure of the CSV. This
condition, if not corrected, could result in an unintended internal
fuel leak during high power demand, leading to reduced fuel flow and
potential thrust shortfalls and, combined with a loss of the second
engine, could result in reduced control of the airplane.
The FAA is proposing this AD to address the unsafe condition on
these products.
You may examine the MCAI in the AD docket at <a href="http://regulations.gov">regulations.gov</a>under
Docket No. FAA-2026-8807.
Material Incorporated by Reference Under 1 CFR Part 51
EASA AD 2025-0183 specifies procedures for replacing an HMU having
part number (P/N) G5000HMU02 or P/N G5000HMU03 with a serviceable HMU
before reaching a reduced life limit. EASA AD 2025-0183 also limits the
installation of affected parts under certain conditions. 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.
FAA's Determination
These products have been approved by the civil aviation authority
of another country and are approved for operation in the United States.
Pursuant to the FAA's bilateral agreement with this State of Design
Authority, that authority has notified the FAA of the unsafe condition
described in the MCAI referenced above. The FAA is issuing this NPRM
after determining that the unsafe condition described previously is
likely to exist or develop in other products of the same type design.
Proposed AD Requirements in This NPRM
This proposed AD would require accomplishing the actions specified
in EASA AD 2025-0183 described previously, except for any differences
identified as exceptions in the regulatory text of this proposed AD.
Explanation of Required Compliance Information
In the FAA's ongoing efforts to improve the efficiency of the AD
process, the FAA developed a process to use some civil aviation
authority (CAA) ADs as the primary source of information for compliance
with requirements for corresponding FAA ADs. The FAA has been
coordinating this process with manufacturers and CAAs. As a result, the
FAA proposes to incorporate EASA AD 2025-0183 by reference in the FAA
final rule. This proposed AD would, therefore, require compliance with
EASA AD 2025-0183 in its entirety through that incorporation, except
for any differences identified as exceptions in the regulatory text of
this proposed AD. Using common terms that are the same as the heading
of a particular section in EASA AD 2025-0183 does not mean that
operators need comply only with that section. For example, where the AD
requirement refers to ``all required actions and compliance times,''
compliance with this AD requirement is not limited to the section
titled ``Required Action(s) and Compliance Time(s)'' in EASA AD 2025-
0183. Material required by EASA AD 2025-0183 for compliance will be
available at <a href="http://regulations.gov">regulations.gov</a> under Docket No. FAA-2026-8807 after the
FAA final rule is published.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would
affect 38 airplanes of U.S. registry. The FAA estimates the following
costs to comply with this proposed AD:
Estimated Costs for Required Actions *
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Labor cost Parts cost Cost per product Cost on U.S. operators
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Up to 20 work-hours x $85 per hour = Up to $2,081,930....... Up to $2,083,630....... Up to $79,177,940.
$1,700.
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* The estimated labor and parts cost is for the installation of two new HMUs per airplane (one HMU per engine).
The FAA has no definitive data on which to base the cost estimate for the installation of an overhauled HMU.
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
[[Page 60035]]
(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:
Airbus SAS: Docket No. FAA-2026-8807; Project Identifier MCAI-2025-
01385-T.
(a) Comments Due Date
The FAA must receive comments on this airworthiness directive
(AD) by November 6, 2026.
(b) Affected ADs
None.
(c) Applicability
This AD applies to Airbus SAS Model A350-941 airplanes,
certificated in any category, as identified in European Union
Aviation Safety Agency (EASA) AD 2025-0183, dated August 25, 2025
(EASA AD 2025-0183).
(d) Subject
Air Transport Association (ATA) of America Code 73, Engine Fuel
and Control.
(e) Unsafe Condition
This AD was prompted by reports of engine health monitoring
messages requiring premature removal of hydro-mechanical units. The
FAA is issuing this AD to address wear-induced stiction within the
combining spill valve of the engine hydro-mechanical units (HMU),
which could result in an unintended internal fuel leak during high
power demand, leading to reduced fuel flow and potential thrust
shortfalls and, combined with a loss of the second engine, could
result in reduced control of the airplane.
(f) Compliance
Comply with this AD within the compliance times specified,
unless already done.
(g) Requirements
Except as specified in paragraph (h) of this AD: Comply with all
required actions and compliance times specified in, and in
accordance with, EASA AD 2025-0183.
Note 1 to paragraph (g): Guidance for determining the current
HMU life can be found in paragraph 1.E.(2), ``Accomplishment
Timescale'' in Airbus Service Bulletin A350-73-P019, dated July 15,
2025. Operators may also contact Rolls-Royce for guidance on
determining the current HMU life.
(h) Exceptions to EASA AD 2025-0183
(1) Where EASA AD 2025-0183 refers to its effective date, this
AD requires using the effective date of this AD.
(2) Where paragraph (1) of EASA AD 2025-0183 specifies to
replace the affected part before exceeding the applicable life limit
defined in Table 1 of EASA AD 2025-0183: For this AD, replace the
affected part before exceeding the applicable life limit defined in
Table 1 of EASA AD 2025-0183, or within 30 days after the effective
date of this AD, whichever occurs later.
(3) If the flight hours accumulated on the affected HMU since
new (first installation on the airplane) or since last overhaul
cannot be determined, it must be assumed that the HMU has
accumulated the applicable time specified in paragraph (h)(3)(i) or
(ii) of this AD.
(i) For an affected HMU installed on a Rolls-Royce Trent XWB-84
engine or Trent XWB-75 engine: 35,000 flight hours.
(ii) For an affected HMU installed on a Rolls-Royce Trent XWB-
84EP engine: 26,500 flight hours.
(4) This AD does not adopt the ``Remarks'' section of EASA AD
2025-0183.
(i) Additional AD Provisions
The following provisions also apply to this AD:
(1) Alternative Methods of Compliance (AMOCs): 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 (j)(1) of this AD and email to:
<a href="/cdn-cgi/l/email-protection#72333f3d31321413135c151d04"><span class="__cf_email__" data-cfemail="9ddcd0d2deddfbfcfcb3faf2eb">[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) Contacting the Manufacturer: For any requirement in this AD
to obtain instructions from a manufacturer, the instructions must be
accomplished using a method approved by the Manager, AIR-520,
Continued Operational Safety Branch, FAA; or EASA; or Airbus SAS's
EASA Design Organization Approval (DOA). If approved by the DOA, the
approval must include the DOA-authorized signature.
(3) Required for Compliance (RC): Except as required by
paragraph (i)(2) of this AD, if any material contains procedures or
tests that are identified as RC, those procedures and tests must be
done to comply with this AD; any procedures or tests that are not
identified as RC are recommended. Those procedures and tests that
are not identified 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 procedures and
tests identified as RC can be done and the airplane can be put back
in an airworthy condition. Any substitutions or changes to
procedures or tests identified as RC require approval of an AMOC.
(j) Additional Information
(1) For more information about this AD, contact Anthony Decaro,
Aviation Safety Engineer, FAA, 2200 South 216th St., Des Moines, WA
98198; phone: 562-627-5374; email: <a href="/cdn-cgi/l/email-protection#caaba4bea2a5a4b3e4aee4aeafa9abb8a58aacababe4ada5bc"><span class="__cf_email__" data-cfemail="7819160c10171601561c561c1d1b190a17381e1919561f170e">[email protected]</span></a>.
(2) For Airbus SAS material identified in this AD that is not
incorporated by reference, contact Airbus SAS, Airworthiness
Office--EAL, Rond-Point Emile Dewoitine No: 2, 31700 Blagnac Cedex,
France; telephone +33 5 61 93 36 96; fax +33 5 61 93 45 80; email
<a href="/cdn-cgi/l/email-protection#0b6864657f62657e6e6f266a62797c64797f6362656e7878256a383e3b4b376a2b63796e6d36" http: airbus.com">airbus.com</a>">continued-airworthiness.a350@<a href="http://airbus.com">airbus.com</a></a>; website <a href="http://airbus.com">airbus.com</a>.
(k) 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 this AD specifies otherwise.
(i) European Union Aviation Safety Agency (EASA) AD 2025-0183,
dated August 25, 2025.
(ii) [Reserved]
(3) For EASA material identified in this AD, contact EASA,
Konrad-Adenauer-Ufer 3, 50668 Cologne, Germany; telephone +49 221
8999 000; email <a href="/cdn-cgi/l/email-protection#ffbebb8cbf9a9e8c9ed19a8a8d908f9ed19a8a"><span class="__cf_email__" data-cfemail="f4b5b087b491958795da9181869b8495da9181">[email protected]</span></a>. You may find this material on
the EASA website at ad.easa.europa.eu.
(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#bcdace92d5d2cfccd9dfc8d5d3d2fcd2ddcedd92dbd3ca"><span class="__cf_email__" data-cfemail="264054084f4855564345524f4948664847544708414950">[email protected]</span></a>.
Issued on September 15, 2026.
Brian Knaup,
Acting Deputy Director, Integrated Certificate Management Division,
Aircraft Certification Service.
[FR Doc. 2026-19360 Filed 9-21-26; 8:45 am]
BILLING CODE 4910-13-P
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