# [Amended]
**AGENCY:**
Federal Aviation Administration (FAA), DOT.
**ACTION:**
Notice of proposed rulemaking (NPRM).
**SUMMARY:**
The FAA proposes to adopt a new airworthiness directive (AD) for all Airbus Helicopters Model AS355E, AS 355-F, AS 355-F1, AS355F2, and AS355N helicopters. This proposed AD was prompted by reports of cracks in the legs of the side supports of the tail rotor transmission fan. This proposed AD would require repetitively inspecting the side supports of the tail rotor transmission fan for cracks and, depending on the results, replacing both side supports. The FAA is proposing this AD to address the unsafe condition on these products.
**DATES:**
The FAA must receive comments on this NPRM by November 14, 2025.
**ADDRESSES:**
You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:
• *Federal eRulemaking Portal:* Go to *regulations.gov* . Follow the instructions for submitting comments.
• *Fax:* (202) 493-2251.
• *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.
• *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 *regulations.gov* under Docket No. FAA-2025-3420; 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:*
• For European Union Aviation Safety Agency (EASA) material identified in this proposed AD, contact EASA, Konrad-Adenauer-Ufer 3, 50668 Cologne, Germany; phone: +49 221 8999 000; email: *[email protected];* website: *easa.europa.eu.* You may find this material on the EASA website at *ad.easa.europa.eu.*
• 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. It is also available at *regulations.gov* under Docket No. FAA-2025-3420.
**FOR FURTHER INFORMATION CONTACT:**
Kim-Anh Tran, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (316) 946-4190; email: *[email protected]* .
**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-2025-3420; Project Identifier MCAI-2025-00225-R” 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 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 Kim-Anh Tran, 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**
EASA, which is the Technical Agent for the Member States of the European Union, has issued EASA AD 2025-0052, dated February 28, 2025 (EASA AD 2025-0052) (also referred to as the MCAI), to correct an unsafe condition on all Airbus Helicopters Model AS 355 E, AS 355 F, AS 355 F1, AS 355 F2, and AS 355 N helicopters. The MCAI states there have been reports, following scheduled maintenance, of cracks in the legs of the left hand (LH) and right hand (RH) side supports of the tail rotor transmission fan installed on helicopters with the post-mod 07-9062 configuration. This condition, if not addressed, could result in failure of the legs supporting the tail rotor transmission fan and displacement of the tail rotor transmission fan assembly, which could lead to the loss of the engine and main gearbox cooling function, loss of the tail rotor drive, and consequent loss of control of the helicopter.
The FAA is issuing this AD to detect and correct a cracked side support of the tail rotor transmission fan.
You may examine the MCAI in the AD docket at *regulations.gov* under Docket No. FAA-2025-3420.
**Material Incorporated by Reference Under 1 CFR Part 51**
The FAA reviewed EASA AD 2025-0052, which specifies procedures for repetitive inspections of the LH and RH side supports of the tail rotor transmission fan, having part number (P/N) 355A34104006 (LH) and P/N 355A34104106 (RH) respectively, for cracks and, if any crack is found on any side support, replacement of both side supports. EASA AD 2025-0052 also specifies reporting the inspection results to the manufacturer. 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 (CAA) 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 on 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 2025-0052, described previously, as incorporated by reference, except for any differences identified as exceptions in the regulatory text of this proposed AD. See “Differences Between this Proposed AD and the MCAI” for a discussion of the general differences included in this proposed AD.
**Differences Between This Proposed AD and the MCAI**
The MCAI requires reporting inspection results to the manufacturer, whereas this proposed AD would not.
**Interim Action**
The FAA considers that this proposed AD would be an interim action. The manufacturer is still investigating the root cause of the unsafe condition identified in this AD. If final action is later identified, the FAA might consider further rulemaking.
**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 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 incorporates EASA AD 2025-0052 by reference in the FAA final rule. This proposed AD would, therefore, require compliance with EASA AD 2025-0052 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 2025-0052 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 2025-0052. Material referenced in EASA AD 2025-0052 for compliance will be available at *regulations.gov* under Docket No. FAA-2025-3420 after the FAA final rule is published.
**Costs of Compliance**
The FAA estimates that this AD, if adopted as proposed, would affect 38 helicopters of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:
| Action | Labor cost | Parts cost | Cost per | Cost on U.S. |
| --- | --- | --- | --- | --- |
| Inspect both side supports | 1.5 work-hours × $85 per hour = $128 | $0 | $128 | $4,864 |
The FAA estimates the following costs to do any necessary on-condition actions that would be required based on the results of the proposed inspection. The agency has no way of determining the number of helicopters that might need these on-condition actions:
| Action | Labor cost | Parts cost | Cost per |
| --- | --- | --- | --- |
| Replace both side supports | 24 work-hours × $85 per hour = $2,040 | $600 | $2,640 |
**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**
1. The authority citation for part 39 continues to read as follows:
**Authority:**
49 U.S.C. 106(g), 40113, 44701.
§ 39.13
2. The FAA amends § 39.13 by adding the following new airworthiness directive:
*Airbus Helicopters:* Docket No. FAA-2025-3420; Project Identifier MCAI-2025-00225-R.
**(a) Comments Due Date**
The FAA must receive comments on this airworthiness directive (AD) by November 14, 2025.
**(b) Affected ADs**
None.
**(c) Applicability**
This AD applies to Airbus Helicopters Model AS355E, AS 355-F, AS 355-F1, AS355F2, and AS355N helicopters, certificated in any category.
**(d) Subject**
Joint Aircraft System Component (JASC) Code 6500, Tail Rotor Drive System.
**(e) Unsafe Condition**
This AD was prompted by reports of cracks in the legs of the side support of the tail rotor transmission fan. The FAA is issuing this AD to detect and correct a cracked side support of the tail rotor transmission fan. The unsafe condition, if not addressed, could result in failure of the legs supporting the tail rotor transmission fan and displacement of the tail rotor transmission fan assembly, which could lead to the failure of the engine and main gearbox cooling function, loss of the tail rotor drive, and consequent loss of 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 2025-0052, dated February 28, 2025 (EASA AD 2025-0052).
**(h) Exceptions to EASA AD 2025-0052**
(1) Where EASA AD 2025-0052 requires compliance in terms of flight hours, this AD requires using hours time-in-service.
(2) Where EASA AD 2025-0052 refers to its effective date, this AD requires using the effective date of this AD.
(3) Where paragraph (2) of EASA AD 2025-0052 specifies “replace both affected parts in accordance with the instructions of the ASB”, this AD requires replacing that text with “remove both affected parts from service and replace with new (zero hours time-in-service) parts in accordance with the instructions of the ASB”.
(4) This AD does not adopt the “Remarks” section of EASA AD 2025-0052.
**(i) No Reporting Requirement**
Although EASA AD 2025-0052 and the material referenced in EASA AD 2025-0052 specify to submit certain information to the manufacturer, this AD does not include that requirement.
**(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: *[email protected].*
(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 Kim-Anh Tran, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (316) 946-4190; email: *[email protected].*
**(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 2025-0052, dated February 28, 2025.
(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: *[email protected];* 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 *[email protected].*
Issued on September 26, 2025.
Steven W. Thompson,
Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.