Proposed Rule2026-09801
Airworthiness Directives; Stemme GmbH Gliders
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
May 15, 2026
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
The FAA proposes to adopt a new airworthiness directive (AD) for all Stemme GmbH (Stemme) Model Stemme S 12 gliders. This proposed AD was prompted by reports of fuel leaking around certain copper sealing rings within the fuel system. This proposed AD would require repetitive visual checks of the fuel system for fuel leakage, and replacement of the affected copper sealing ring. This proposed AD would also prohibit the installation of affected parts. 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 94 (Friday, May 15, 2026)</title>
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[Federal Register Volume 91, Number 94 (Friday, May 15, 2026)]
[Proposed Rules]
[Pages 27876-27878]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-09801]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2026-4637; Project Identifier MCAI-2025-01226-G]
RIN 2120-AA64
Airworthiness Directives; Stemme GmbH Gliders
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 Stemme GmbH (Stemme) Model Stemme S 12 gliders. This proposed
AD was prompted by reports of fuel leaking around certain copper
sealing rings within the fuel system. This proposed AD would require
repetitive visual checks of the fuel system for fuel leakage, and
replacement of the affected copper sealing ring. This proposed AD would
also prohibit the installation of affected parts. The FAA is proposing
this AD to address the unsafe condition on these products.
DATES: The FAA must receive comments on this NPRM by June 29, 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-2026-4637; 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 Stemme material identified in this proposed AD,
contact Stemme, Flugplatzstrasse F2 Nr. 6-7, Strausberg, Germany 15344;
phone: +49 (0) 3341 3612; email: <a href="/cdn-cgi/l/email-protection#43222a31342c31372b2a2d263030037f22632b3126257e" http: stemme.com">stemme.com</a>">airworthiness@<a href="http://stemme.com">stemme.com</a></a>; website:
<a href="http://stemme.com">stemme.com</a>.
<bullet> You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 1100 Main, Kansas City, MO
64105. For information on the availability of this material at the FAA,
call (817) 222-5110.
FOR FURTHER INFORMATION CONTACT: George Weir, Aviation Safety Engineer,
FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (817)
222-4045; email: <a href="/cdn-cgi/l/email-protection#0e696b617c696b206f20796b677c4e686f6f20696178"><span class="__cf_email__" data-cfemail="3f585a504d585a115e11485a564d7f595e5e11585049">[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 ADDRESSES. Include ``Docket No. FAA-2026-4637; Project Identifier
MCAI-2025-01226-G'' 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
[[Page 27877]]
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
George Weir, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite
410, Westbury, NY 11590. Any commentary that the FAA receives which is
not specifically designated as CBI will be placed in the public docket
for this rulemaking.
Background
The European Union Aviation Safety Agency (EASA), which is the
Technical Agent for the Member States of the European Union, has issued
EASA AD 2025-0155, dated July 21, 2025 (referred to as the MCAI), to
correct an unsafe condition on Stemme Model Stemme S 12 gliders. The
MCAI states that occurrences of fuel leaks at multiple locations within
the fuel system have been reported. To address the unsafe condition,
Stemme published service material to provide replacement instructions
for affected copper sealing rings, and a parts installation
restriction. This condition, if not addressed, could result in an in-
flight fire.
All of the affected airplanes were produced and delivered with the
affected copper sealing rings installed.
You may examine the MCAI in the AD docket at <a href="http://regulations.gov">regulations.gov</a> under
Docket No. FAA-2026-4637.
Material Incorporated by Reference Under 1 CFR Part 51
The FAA reviewed Stemme Service Bulletin (SB) P062-980082 Revision
01, dated July 15, 2025. This material specifies procedures for
replacement of affected copper sealing rings within the fuel pump set
assembly and drainer complete assembly.
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 and material referenced above. 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.
Proposed AD Requirements in This NPRM
This proposed AD would require repetitive visual checks of the fuel
system for fuel leakage (staining, wetness, dripping, etc.) and
replacement of the affected copper sealing rings if leakage is
detected. This proposed AD would also prohibit the installation of
affected parts.
The owner/operator (pilot) holding at least a private pilot
certificate may perform the visual check and must enter compliance with
the applicable paragraph of this AD into the glider maintenance records
in accordance with 14 CFR 43.9(a) and 91.417(a)(2)(v). The pilot may
perform this action because it only involves visually checking affected
locations for fuel leakage. This action could be performed equally well
by a pilot or a mechanic. This is an exception to the FAA's standard
maintenance regulations.
Costs of Compliance
The FAA estimates that this AD, if adopted as proposed, would
affect 31 gliders 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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Visual check of fuel system........... 1 work-hour x $85 per $0 $85 $2,635
hour = $85.
Replacement of copper sealing rings... 2 work-hours x $85 per 150 320 9,920
hour = $170.
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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:
[[Page 27878]]
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:
Stemme GmbH: Docket No. FAA-2026-4637; Project Identifier MCAI-2025-
01226-G.
(a) Comments Due Date
The FAA must receive comments on this airworthiness directive
(AD) by June 29, 2026.
(b) Affected ADs
None.
(c) Applicability
This AD applies to all Stemme GmbH Model Stemme S 12 gliders,
certificated in any category.
Note to paragraph (c): All of the affected airplanes were
produced and delivered with the affected copper sealing rings
installed.
(d) Subject
Joint Aircraft System Component (JASC) Code 2800, Aircraft Fuel
System.
(e) Unsafe Condition
This AD was prompted by reports of fuel leaking around certain
copper sealing rings within the fuel system. The FAA is issuing this
AD to prevent fuel leakage in the fuel system. The unsafe condition,
if not addressed, could result in an in-flight fire.
(f) Compliance
Comply with this AD within the compliance times specified,
unless already done.
(g) Definitions
For the purpose of this AD, the definitions in paragraphs (g)(1)
through (4) of this AD apply.
(1) An ``affected location'' is any of the following:
(i) The copper sealing ring within the fuel pump set assembly
having part number (P/N) 128201, between the screw-in adapter having
P/N 831099 and the fuel distributor having P/N 128229, and between
the screw-in adapter having P/N 831099 and the fuel distributor
having P/N 128228. The fuel pump set assembly P/N 128201 is located
at the front left area of the middle fuselage and may be accessed
from below when the main landing gear is extended. (Location defined
in Stemme Service Bulletin (SB) P062-980082 Revision 01, dated July
15, 2025, Page 1 of 3, Action 2 and Figure 1)
(ii) The copper sealing ring within the drainer complete having
P/N 128207, between the screw-in adapter having P/N 831099 and the
drainer attachment having P/N 128271. The drainer complete P/N
128207 is located at the main landing gear bay and may be accessed
from below when the main landing gear is extended. (Location defined
in Stemme SB P062-980082 Revision 01, dated July 15, 2025, Page 2 of
3, Action 3 and Page 3 of 3 Figure 2)
(2) An ``affected part'' is a copper sealing ring having P/N
D7603-12016-CU.
(3) ``Group 1 gliders'' are gliders that have an affected part
installed.
(4) ``Group 2 gliders'' are gliders that do not have an affected
part installed.
(h) Required Actions
(1) For Group 1 gliders, before further flight after the
effective date of this AD and thereafter before each flight until
the replacement required by paragraph (h)(2) is accomplished,
perform a visual check using a light source of the affected
locations for indications of fuel leakage (staining, wetness,
dripping, etc). The owner/operator (pilot) holding at least a
private pilot certificate may perform the visual check and must
enter compliance with the applicable paragraph of this AD into the
glider maintenance records in accordance with 14 CFR 43.9(a) and
91.417(a)(2)(v). The record must be maintained as required by 14 CFR
91.417.
(2) For Group 1 gliders, at whichever compliance time in
paragraph (h)(2)(i) or (ii) that occurs first, replace the affected
part at each affected location with a sealing ring having P/N 831984
in accordance with the instructions of Action 2 or Action 3 of
Stemme SB P062-980082, Revision 01, dated July 15, 2025, as
applicable.
(i) Before further flight if any leakage is detected during any
preflight check required by paragraph (h)(1) of this AD.
(ii) Within 100 hours time-in-service after the effective date
of this AD.
(i) Installation Prohibition
For Group 1 and Group 2 gliders: As of the effective date of
this AD, do not install an affected part as defined in paragraph
(g)(2) of this AD on any glider.
(j) Alternative Methods of Compliance (AMOCs)
The Manager, International Validation 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 local Flight
Standards District Office, as appropriate. If sending information
directly to the manager of the International Validation Branch, send
it to the attention of the person identified in paragraph (k) of
this AD and email to: <a href="/cdn-cgi/l/email-protection#4a0b0705090a2c2b2b642d253c"><span class="__cf_email__" data-cfemail="682925272b280e0909460f071e">[email protected]</span></a>. Before using any approved AMOC,
notify your appropriate principal inspector, or lacking a principal
inspector, the manager of the local flight standards district
office/certificate holding district office.
(k) Additional Information
For more information about this AD, contact George Weir,
Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410,
Westbury, NY 11590; phone: (817) 222-4045; email:
<a href="/cdn-cgi/l/email-protection#8aedefe5f8edefa4eba4fdefe3f8caecebeba4ede5fc"><span class="__cf_email__" data-cfemail="e88f8d879a8f8dc689c69f8d819aa88e8989c68f879e">[email protected]</span></a>.
(l) Material Incorporated by Reference
(1) The Director of the Federal Register approved the
incorporation by reference (IBR) 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) Stemme Service Bulletin P062-980082, Revision 01, dated July
15, 2025.
(ii) [Reserved]
(3) For Stemme material identified in this AD, contact Stemme
GmbH, Flugplatzstrasse F2 Nr. 6-7, Strausberg, Germany 15344; phone:
+49 (0) 3341 3612; email: <a href="/cdn-cgi/l/email-protection#7819110a0f170a0c1011161d0b0b38441958100a1d1e45" http: stemme.com">stemme.com</a>">airworthiness@<a href="http://stemme.com">stemme.com</a></a>; website:
<a href="http://stemme.com">stemme.com</a>.
(4) You may view this material at the FAA, Airworthiness
Products Section, Operational Safety Branch, 1100 Main, Kansas City,
MO 64105. For information on the availability of this material at
the FAA, call (817) 222-5110.
(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#1573673b7c7b66657076617c7a7b557b7467743b727a63"><span class="__cf_email__" data-cfemail="0f697d2166617c7f6a6c7b6660614f616e7d6e21686079">[email protected]</span></a>.
Issued on May 12, 2026.
Paul R. Bernado,
Acting Director, Compliance & Airworthiness Division, Aircraft
Certification Service.
[FR Doc. 2026-09801 Filed 5-14-26; 8:45 am]
BILLING CODE 4910-13-P
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