Background The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all AHD Model EC135P1, EC135P2, EC135P2+, EC135P3, EC135T1, EC135T2, EC135T2+, EC635T2+, and EC135T3 helicopters. The NPRM was published in the Federal Register on April 25, 2025 (90 FR 17352). The NPRM was prompted by AD 2023-0197, dated November 10, 2023 (EASA AD 2023-0197) (also referred to as the MCAI), issued by EASA, which is the Technical Agent for the Member States of the European Union. The MCAI advises of reports of ruptured and deformed flexible couplings, and that investigations determined that a flexible coupling installed with high axial displacement causes increased stresses and friction between its sheets. The MCAI states that this unsafe condition, if not detected and corrected, could lead to cracks and extensive deformation of flexible couplings and consequent high vibration of the tail rotor drive shaft, possibly resulting in reduced control of the helicopter. In the NPRM, the FAA proposed to require inspecting the axial displacement of the tail rotor drive shaft and, depending on the results, taking corrective actions including inspecting the flexible couplings. The NPRM also proposed to prohibit installing a tail rotor drive shaft unless certain procedures are followed. The FAA is issuing this AD to address the unsafe condition on these products. You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2025-0629. Discussion of Final Airworthiness Directive Comments The FAA received no comments on the NPRM or on the determination of the costs. Additional Changes Made to This AD The FAA has revised paragraph (h) of this AD to clarify that where paragraphs (4) and (6) of EASA AD 2023-0197 specify replacing the flexible couplings in accordance with the instructions of section 4.1 of the service information referenced, this AD requires replacing the flexible couplings in accordance with the instructions of sections 4.1 and 4.2 of the service information referenced in EASA AD 2023-0197. The FAA has also revised paragraph (h) of this AD to clarify that this AD prohibits installing a tail rotor drive shaft unless certain procedures are followed, as stated in the Preamble of the NPRM. Conclusion 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 reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed. Accordingly, the FAA is issuing this AD to address the unsafe condition on these products. Except for minor editorial changes and any other changes described previously, this AD is adopted as proposed in the NPRM. None of the changes will increase the economic burden on any operator. Material Incorporated by Reference Under 1 CFR Part 51 The FAA reviewed EASA AD 2023-0197, which specifies a one-time inspection of the flexible coupling for axial displacement and, depending on the results, corrective actions. Corrective actions include replacing both flexible couplings and correcting the axial displacement, or inspecting the flexible couplings, replacing each flexible coupling having a discrepancy, and correcting the axial displacement. For certain flexible couplings not replaced based on the results of the flexible coupling inspection, EASA AD 2023-0197 requires replacing the flexible couplings within a longer compliance time. EASA AD 2023-0197 also prohibits installing a tail rotor drive shaft on any helicopter unless certain procedures are followed. 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. Differences Between This AD and the MCAI The MCAI applies to Model EC635 P2+, EC635 P3, EC635 T1, and EC635 T3 helicopters, whereas this AD does not because these models do not have an FAA type certificate. Costs of Compliance The FAA estimates that this AD affects 69 helicopters of U.S. registry. Labor rates are estimated at $85 per hour. Based on these numbers, the FAA estimates the following costs to comply with this AD. Inspecting both flexible couplings for axial displacement will take 8 work-hours for an estimated cost of $680 per helicopter and $46,920 for the U.S. fleet. If required, replacing both flexible couplings will take 2 work-hours, and parts will cost $4,100 for an estimated cost of $4,270 per helicopter. Replacing one flexible coupling will take 1 work-hour and parts will cost $2,050 for an estimated cost of $2,135 per flexible coupling. If required, correcting the axial displacement of the flexible couplings will take 5 work-hours for an estimated cost of $425 per helicopter. 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 This AD will not have federalism implications under Executive Order 13132. This AD will 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 that this AD: (1) Is not a "significant regulatory action" under Executive Order 12866, (2) Will not affect intrastate aviation in Alaska, and (3) Will 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 Amendment Accordingly, under the authority delegated to me by the Administrator, the FAA amends 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: 2026-02-01 Airbus Helicopters Deutschland GmbH: Amendment 39-23237; Docket No. FAA-2025-0629; Project Identifier MCAI-2023-01183-R. (a) Effective Date This airworthiness directive (AD) is effective February 26, 2026. (b) Affected ADs None. (c) Applicability This AD applies to Airbus Helicopters Deutschland GmbH (AHD) Model EC135P1, EC135P2, EC135P2+, EC135P3, EC135T1, EC135T2, EC135T2+, EC635T2+, and EC135T3 helicopters, certificated in any category. Note 1 to paragraph (c): Helicopters with an EC135P3H designation are Model EC135P3 helicopters and helicopters with an EC135T3H designation are Model EC135T3 helicopters. (d) Subject Joint Aircraft System Component (JASC) Code 6510, Tail Rotor Drive Shaft. (e) Unsafe Condition This AD was prompted by reports of ruptured and deformed flexible couplings. The FAA is issuing this AD to detect axial displacement of the tail rotor drive shaft that exceeds allowable limits. The unsafe condition, if not addressed, could result in cracks and extensive deformation of flexible couplings, high vibration of the tail rotor drive shaft, and consequent reduced control of the helicopter. (f) Compliance Comply with this AD within the compliance times specified, unless already done. (g) Requirements Except as specified in paragraphs (h) and (i) of this AD: Comply with all required actions and compliance times specified in, and in accordance with, European Union Aviation Safety Agency AD 2023-0197, dated November 10, 2023 (EASA AD 2023-0197). (h) Exceptions to EASA AD 2023-0197 (1) Where EASA AD 2023-0197 requires compliance in terms of flight hours, this AD requires using hours time-in-service. (2) Where EASA AD 2023-0197 refers to its effective date, this AD requires using the effective date of this AD. (3) Where paragraphs (2) and (6) of EASA AD 2023-0197 state "new", this AD requires replacing that text with "new (zero hours time-in-service)". (4) Where paragraph (4) of EASA AD 2023-0197 states "any discrepancy", for the purpose of this AD, discrepancy may be indicated by cracks, mechanical damage, deformation, delamination, corrosion, loose rivets, or damaged surface protection, where these discrepancies exceed the allowable limits as defined in the material referenced in EASA AD 2023-0197. (5) Where paragraph (4) of EASA AD 2023-0197 states "replace that flexible coupling", this AD requires replacing that text with "replace that flexible coupling with a new (zero hours time-in-service) flexible coupling". (6) Where paragraphs (4) and (6) of EASA AD 2023-0197 state "in accordance with the instructions of section 4.1 of the Accomplishment Procedure of the ASB", this AD requires replacing that text with "in accordance with the instructions of sections 4.1 and 4.2 of the Accomplishment Procedure of the material, referenced in EASA AD 2023-0197". (7) This AD does not adopt the "Remarks" section of EASA AD 2023-0197. (i) No Reporting or Returning of Parts Requirement Although the material referenced in EASA AD 2023-0197 specifies to submit certain information and to send parts to the manufacturer, this AD does not require those actions. (j) Special Flight Permits Special flight permits are prohibited. (k) Alternative Methods of Compliance (AMOCs) (1) 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 (l) of this AD and email to: AMOC@faa.gov. (2) 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. (l) Additional Information For more information about this AD, contact Aaron Nguyen, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (817) 222-5134; email: aaron.t.nguyen@faa.gov. (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) European Union Aviation Safety Agency (EASA) AD 2023-0197, dated November 10, 2023. (ii) [Reserved] (3) For EASA material identified in this AD, contact EASA, Konrad-Adenauer-Ufer 3, 50668 Cologne, Germany; phone: +49 221 8999 000; email: ADs@easa.europa.eu; website: easa.europa.eu. You may find the EASA material on the EASA website at ad.easa.europa.eu. (4) You may view this material at the FAA, Office of the Regional Counsel, Southwest Region, 10101 Hillwood Parkway, Room 6N-321, Fort Worth, TX 76177. 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 . Issued on January 14, 2026. Steven W. Thompson, Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.