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 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 ( printed 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 regulations.gov 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:

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.

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

1. The authority citation for part 39 continues to read as follows:

( printed page 27878) Authority: 49 U.S.C. 106(g), 40113, 44701.

2. The FAA amends § 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: AMOC@faa.gov. 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: george.a.weir@faa.gov.

(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: airworthiness@stemme.com; website: stemme.com.

(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 www.archives.gov/​federal-register/​cfr/​ibr-locations or email fr.inspection@nara.gov.

91 FR 27876