# [Amended]
**AGENCY:**
Federal Aviation Administration (FAA), DOT.
**ACTION:**
Notice of proposed rulemaking (NPRM).
**SUMMARY:**
The FAA proposes to supersede Airworthiness Directive (AD) 2021-20-16, which applies to all Airbus Helicopters Model AS355E, AS 355-F, AS 355-F1, AS355F2, AS355N, and AS355NP helicopters and certain Model AS 350B3 helicopters. AD 2021-20-16 requires repetitive cleaning and visual and detailed inspections of the right-hand side of the vertical fin spar and vertical fin upper attachments for discrepancies (cracking) with corrective action, if necessary. Since the FAA issued AD 2021-20-16, Airbus Helicopters developed a modification of the upper fin assembly. This proposed AD would require the same actions as AD 2021-20-16 and would also require replacement of the upper fin assembly with a modified upper fin assembly, which would constitute terminating action for the repetitive inspections. The FAA is proposing this AD to address the unsafe condition on these products.
**DATES:**
The FAA must receive comments on this NPRM by October 6, 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-2025-1735; 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 Agency (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.*
• 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-2025-1735.
**FOR FURTHER INFORMATION CONTACT:**
Steven Warwick, Aviation Safety Engineer, FAA, 1600 Stewart Ave., Suite 410, Westbury, NY 11590; phone: (817) 222-5225; 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 to an address listed under the *ADDRESSES* section. Include “Docket No. FAA-2025-1735; Project Identifier MCAI-2024-00408-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 the 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 Steven Warwick, Aviation Safety Engineer, FAA, 1600 Stewart Ave., 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 FAA issued AD 2021-20-16, Amendment 39-21754 (86 FR 57550, dated October 18, 2021) (AD 2021-20-16), for Airbus Helicopters Model AS355E, AS 355-F, AS 355-F1, AS355F2, AS355N, and AS355NP helicopters, all serial numbers, and Model AS 350B3 helicopters, all serial numbers except those that have Airbus Helicopters Modification 073148 in production. AD 2021-20-16 was prompted by MCAI originated by EASA, which is the Technical Agent for the Member States of the European Union. EASA issued EASA AD 2021-0099, dated April 9, 2021 (EASA AD 2021-0099), to correct an unsafe condition identified as cracking in the spar of the upper part of the vertical fin and fractures in the front attachment screws.
AD 2021-20-16 requires repetitive cleaning and detailed inspections for cracking of the vertical fin spar and vertical fin upper attachments, and corrective action if necessary. The FAA issued this AD to address cracking in the spar of the upper part of the vertical fin and fractures in the front attachment screws. This condition could lead to in-flight separation of the upper part of the vertical fin, resulting in loss of control of the helicopter.
**Actions Since AD 2021-20-16 Was Issued**
Since the FAA issued AD 2021-20-16, EASA superseded EASA AD 2021-0099 through a series of ADs, the most recent being EASA AD 2024-0139, dated July 12, 2024 (EASA AD 2024-0139) (also referred to as “the MCAI”). EASA AD 2024-0139 states that after a further occurrence of a crack on a Model AS355NP helicopter, EASA concluded there was a need to temporarily reduce the never-exceed-speed (V <sub>NE</sub> ) for all AS355 helicopters. In addition, Airbus Helicopters developed a reinforced upper fin assembly and published service information that provides instructions for this modification. EASA AD 2024-0139 retains the repetitive inspections and V <sub>NE</sub> limitations in its previous ADs and also requires modification of the helicopter with the reinforced upper fin assembly, which is terminating action for inspections and limitations.
You may examine the MCAI in the AD docket at *regulations.gov* under Docket No. FAA-2025-1735.
**Material Incorporated by Reference Under 1 CFR Part 51**
The FAA reviewed EASA AD 2024-0139, which specifies procedures for amending the rotorcraft flight manual (RFM) and installing a placard to add a speed limitation. EASA AD 2024-0139 allows exceeding the speed limitation on certain maintenance flights and specifies accomplishing an inspection after each flight where the speed is exceeded. EASA AD 2024-0139 also requires repetitively inspecting the right-hand external side around the two top screws of certain upper fin spars for a crack. EASA AD 2024-0139 specifies that installing an upper fin assembly P/N 355A14-0522-1751 constitutes terminating action for the repetitive inspection requirements and the speed limitations. Lastly, EASA AD 2024-0139 prohibits installing affected upper fin assemblies on any helicopter.
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 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, it 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 2024-0139, 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 general discussion of these differences.
**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 2024-0139 by reference in the FAA final rule. This proposed AD would, therefore, require compliance with EASA AD 2024-0139 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 2024-0139 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 2024-0139. Material referenced in EASA AD 2024-0139 for compliance will be available at *www.regulations.gov* by searching for and locating Docket No. FAA-2025-1735 after the FAA final rule is published.
**Differences Between This Proposed AD and the MCAI**
While the service material referenced in EASA AD 2024-0139 requires accomplishing dye penetrant inspections, this proposed AD would require a dye penetrant inspection (DPI) if the affected part has previously been inspected by a DPI method; otherwise, this proposed AD would require a fluorescent penetrant inspection (FPI).
Where EASA AD 2024-0139 and the service material referenced in EASA AD 2024-0139 specify contacting Airbus Helicopters for repair instructions, this proposed AD would require using a method approved by the FAA, EASA, or Airbus Helicopters' EASA Design Organization Approval.
EASA AD 2024-0139 requires informing all flight crew and operating the helicopter accordingly, whereas this proposed AD would not because those actions are already required by FAA regulations.
EASA AD 2024-0139 allows a pilot to perform some actions, and this proposed AD would not.
**Costs of Compliance**
The FAA estimates that this AD, if adopted as proposed, would affect 650 helicopters of U.S. registry. Labor rates are estimated at $85 per work-hour. Based on these numbers, the FAA estimates the following costs to comply with this proposed AD.
Amending the RFM and installing a placard to incorporate a speed limitation would take approximately 1 work-hour and parts would cost $25 for an estimated cost of $110 per helicopter and $71,500 for the U.S. fleet.
Cleaning and inspecting the vertical fin spar would take 2.5 work-hours for an estimated cost of $213 per helicopter and $138,450 for the U.S. fleet, per inspection cycle.
Modifying the upper fin spar would take 19 work-hours and parts would cost $25,360 for an estimated cost of $26,975 per helicopter and $17,533,750 for the U.S. fleet.
If required, performing a DPI or FPI on the upper fin spar would take 1 work-hour for an estimated cost of $85 per helicopter.
The extent of damage found during the required inspection of the vertical fin spar could vary significantly from helicopter to helicopter. The agency has no way of determining how much damage may be found during these inspections, the cost to repair damaged parts of each helicopter, or the number of helicopters that might need these repairs.
The FAA has included all known costs in its cost estimate. According to the manufacturer, however, some of the costs of this proposed AD may be covered under warranty, thereby reducing the cost impact on affected operators.
**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 that the 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:
a. Removing Airworthiness Directive 2021-20-16, Amendment 39-21754 (86 FR 57550, dated October 18, 2021); and
b. Adding the following new airworthiness directive:
*Airbus Helicopters:* Docket No. FAA-2025-1735; Project Identifier MCAI-2024-00408-R.
**(a) Comments Due Date**
The FAA must receive comments on this airworthiness directive (AD) by October 6, 2025.
**(b) Affected ADs**
This AD replaces AD 2021-20-16, Amendment 39-21754 (86 FR 57550, dated October 18, 2021).
**(c) Applicability**
This AD applies to Airbus Helicopters Model AS 350B3, AS355E, AS 355-F, AS 355-F1, AS355F2, AS355N, and AS355NP helicopters, certificated in any category, as identified in European Union Aviation Safety Agency AD 2024-0139, dated July 12, 2024 (EASA AD 2024-0139).
**(d) Subject**
Joint Aircraft System Component (JASC) Code 5531, Vertical Stabilizer, Spar/Rib Structure.
**(e) Unsafe Condition**
This AD was prompted by a report of a structural crack in the vertical attachment spar of the upper tail fin and fractures in its two front attachment screws. The FAA is issuing this AD to address cracking in the upper fin spar and fracturing of the front attachment screws. The unsafe condition, if not addressed, could result in in-flight separation of the upper part of the vertical fin and subsequent 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, EASA AD 2024-0139.
**(h) Exceptions to EASA AD 2024-0139**
(1) Where EASA AD 2024-0139 requires compliance in terms of flight hours, this AD requires using hours time-in-service.
(2) Where EASA AD 2024-0139 refers to its effective date or to any of the dates listed in paragraphs (h)(2)(i) through (iv) of this AD, this AD requires using the effective date of this AD.
(i) July 12, 2017 (the effective date of EASA AD 2017-0114, dated June 28, 2017).
(ii) April 23, 2021 (the effective date of EASA AD 2021-0099, dated April 9, 2021).
(iii) April 14, 2023 (the effective date of EASA AD 2023-0075, dated April 7, 2023).
(iv) May 18, 2023 (the effective date of EASA AD 2023-0089, dated May 4, 2023).
(3) Where paragraph (1) of EASA AD 2024-0139 specifies to inform all flight crew and operate the helicopter accordingly, this AD does not require those actions.
(4) Although the service material referenced in EASA AD 2024-0139 allows some actions to be performed by a pilot, this AD does not.
(5) Where the service material referenced in EASA AD 2024-0139 states “if you are not sure”, this AD requires replacing that text with “to confirm suspected cracks (scratch, line, misalignment, etc.)”.
(6) Where the service material referenced in EASA AD 2024-0139 states to do a dye-penetrant inspection (DPI), this AD requires the actions in paragraph (h)(6)(i), (ii), or (iii) of this AD, as applicable:
(i) If the right-hand (RH) side of the spar (a) has previously been inspected by a DPI method, accomplish a DPI of the RH side of the spar (a).
(ii) If the RH side of the spar (a) has not previously been inspected by a DPI, accomplish a fluorescent penetrant inspection (FPI) of the RH-hand side of the spar (a), instead of a DPI.
(iii) If you cannot determine whether the RH side of the spar (a) has previously been inspected by a DPI, clean all surfaces to be inspected and accomplish an FPI of the RH side of the spar (a) instead of a DPI.
*Note 1 to paragraph (h)(6)(iii):* Work Card 20-02-09-101 (MTC) contains DPI information related to this AD.
*Note 2 to paragraph (h)(6)(iii):* When entering compliance with the applicable paragraph of the AD into the helicopter maintenance records, explicitly documenting that a dye penetrant inspection was performed improves the accuracy of maintenance records regarding use of dye penetrant inspection dye.
(7) Where the service material referenced in EASA AD 2024-0139 refers to damage, for this AD, damage is defined as looseness, corrosion, broken or missing lockwire, loss of protective surface finish, deformation, fracture, crack, or nick.
(8) Where paragraph (8) of EASA AD 2024-0139 states “maintenance flight”, this AD requires replacing that text with “flight to perform an operational check as specified in 14 CFR 91.407”.
(9) Where paragraph (10) of EASA AD 2024-0139 and the service material referenced in EASA AD 2024-0139 specify contacting Airbus Helicopters for repair instructions, this AD requires using a repair method approved by the FAA, EASA, or Airbus Helicopters' EASA Design Organization Approval (DOA). If approved by the DOA, the approval must include the DOA-authorized signature.
(10) Where the service material referenced in EASA AD 2024-0139 specifies to discard parts, this AD requires removing these parts from service.
(11) Where paragraph (16) of EASA AD 2024-00139 only allows credit for the initial actions in paragraphs (4) through (9) of EASA AD 2024-00139, this AD allows credit for any action in paragraphs (4) through (9) of EASA AD 2024-00139.
(12) This AD does not adopt the “Remarks” section of EASA AD 2024-0139.
**(i) No Reporting Requirement**
Although the material referenced in EASA AD 2024-0139 specifies to submit certain information to the manufacturer, this AD does not require that action.
**(j) 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 (k) 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.
**(k) Additional Information**
For more information about this AD, contact Steven Warwick, Aviation Safety Engineer, FAA, 1600 Stewart Ave., Suite 410, Westbury, NY 11590; phone: (817) 222-5225; email: *[email protected].*
**(l) 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 2024-0139, dated July 12, 2024.
(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 Pkwy., 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 August 18, 2025.
Steven W. Thompson,
Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.