SUPPLEMENTARY INFORMATION:

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 Airbus Helicopters Model AS355E, AS355F, AS355F1, AS355F2, and AS355N helicopters. The NPRM was published in the Federal Register on September 30, 2025 (90 FR 46773). The NPRM was prompted by EASA AD 2025-0052, dated February 28, 2025 (EASA AD 2025-0052) (also referred to as the MCAI), issued by EASA, which is the Technical Agent for the Member States of the European Union. 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-modification 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 failure of the engine and main gearbox cooling function, loss of the tail rotor drive, and consequent loss of control of the helicopter.

In the NPRM, the FAA proposed to 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 issuing this AD to address the unsafe condition of these products.

You may examine the MCAI in the AD docket at regulations.gov under Docket No. FAA-2025-3420.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from five commenters. The comments were from the Citizens Rulemaking Alliance, Elite Rotorcraft, Heli Chicago, and two individuals. The two individuals supported the NPRM without change. The following presents the comments received on the NPRM and the FAA's response to each comment.

Request To Withdraw the Proposed AD

Elite Rotorcraft and Heli Chicago stated that the unsafe condition can be derived from improper maintenance being performed and not following the manufacturer's recommended balancing guidelines. Elite Rotorcraft and Heli Chicago stated they keep their fans balanced, which helps eliminate vibrations that cause cracks. Additionally, both commenters stated that the proposed AD is not warranted unless it addresses the core cause of the unsafe condition, which is the vibration level of the fan. The commenters stated that addressing the vibration level of the fan would eliminate the unsafe condition of cracking. Furthermore, Elite Rotorcraft and Heli Chicago requested that the FAA provide additional data and information relating to the unsafe condition.

The FAA disagrees with the commenters' suggestion that the proposed AD is not warranted. Under 14 CFR part 39, the FAA issues an airworthiness directive when an unsafe condition exists in the product, and the condition is likely to exist or develop in other products of the same type design. Multiple instances have been reported where, during scheduled maintenance, cracks or failures were discovered in the legs of both the LH and RH tail rotor supports. There is currently no definitive evidence that the unsafe condition is related to improper maintenance. The fact that the individual aircraft owned or operated by some commenters have not experienced cracking does not negate the existence of an unsafe condition that exists or may develop on these helicopters. Failure to detect and correct these cracks could cause the loss of all four support legs, displacing the fan assembly. This risks losing engine and main gearbox cooling, tail rotor drive, and overall helicopter control.

Additionally, since Airbus Helicopters is still investigating the root cause of the cracking, at this time the FAA has not determined that the root cause of the cracking is fan vibration. As noted, the FAA considers this AD to be an interim action to detect and correct the unsafe condition. Should a final corrective action be identified in the future, the FAA will consider further rulemaking.

The FAA did not change this AD as a result of this comment.

Request To Justify Forgoing Notice and Comment or Issue an NPRM

The Citizens Rulemaking Alliance requested that the FAA either provide its justification for finding good cause to bypass notice and comment procedures, convert this action to an NPRM, or stay enforcement to allow comments to substantiate the “before further flight” compliance time. The commenter asserted the FAA has not adequately justified use of the good cause exemption to bypass notice and comment and the 30-day delayed effective date.

The FAA notes the comment was submitted in response to an NPRM for which the FAA provided a 45-day comment period. This final rule is effective 35 days after its publication in the Federal Register . Therefore, the FAA did not change this AD as a result of this comment.

Request To Make Incorporation by Reference (IBR) Materials Reasonably Available

The Citizens Rulemaking Alliance stated that the FAA's current practices for IBR frequently fail to meet the legal and regulatory standards for reasonable availability. The commenter called on the FAA to guarantee that all IBR materials are easily and freely accessible to the public in the AD docket and affected parties for both commenting and compliance purposes. They also requested that the FAA reopen the comment period for at least 30 days ( printed page 52233) after access to the IBR material is provided.

The FAA notes that this AD only incorporates by reference EASA AD 2025-0052, not the manufacturer service information referenced in that EASA AD. The FAA posted EASA AD 2025-0052 to the AD docket when the NPRM was published in the Federal Register . The material referenced in EASA AD 2025-0052 may only be posted before the final rule's publication if it is already publicly available or if there is written consent from the owner of that material. Additionally, the FAA provided notice in the NPRM that the material referenced in EASA AD 2025-0052 will be available in the AD docket after this AD is published. Therefore, the FAA did not change this AD as a result of this comment.

Request To Comply With the Paperwork Reduction Act (PRA)

The Citizens Rulemaking Alliance requested that the FAA revise the AD to comply with the PRA if reporting is required or suspend the reporting requirement until PRA requirements are satisfied and then provide an opportunity to comment on the economic burden.

The FAA notes that paragraph (i) of this AD specifies that this AD does not require reporting. If an AD were to require reporting, the preamble of the AD would include a paragraph titled “Paperwork Reduction Act” that would provide the applicable OMB control number, required PRA statements, and the estimated time to collect the required information (burden). Any costs associated with the reporting requirement would be included in the Costs of Compliance section in the preamble of the AD. Therefore, the FAA did not change this AD as a result of this comment.

Request To Consider Impact on Small Entities and To Provide Additional Cost Information

The Citizens Rulemaking Alliance requested that the FAA provide the factual basis for its Regulatory Flexibility Act (RFA) certification that the AD will not have a significant economic impact on a substantial number of small entities. The commenter also requested that the FAA add to the AD docket the cost methodology that supports its conclusion that the AD is not significant under Executive Order 12866. The commenter stated that the FAA's economic analysis should also account for the cost of any downtime and operational impacts.

The FAA recognizes that, in doing the actions required by an AD, operators might incur indirect or incidental costs in addition to the direct costs. The cost analysis in an AD typically describes only the direct costs of the specific actions required by an AD, which does not include indirect or incidental costs such as downtime, loss of revenue, planning, or time necessitated by other administrative actions since those costs might vary significantly among operators. The number of work hours necessary to do the required actions of an AD is provided by the manufacturer. This number represents the time necessary to perform only the actions actually required by an AD. The cost of parts or special tools, if necessary, to complete the actions required by an AD is also provided by the manufacturer. Further, when the FAA is informed that the manufacturer may cover some or all of the estimated costs of an AD under warranty, the FAA indicates that in the AD. In the Costs of Compliance section of the proposed AD, the FAA disclosed the number of affected helicopters on the U.S. registry (updated in this final rule) and the manufacturer-provided number of work hours and cost of parts necessary to complete repairs. Additionally, the FAA determined that this AD will not trigger downtime costs because the requirements of this AD can be performed during regularly scheduled maintenance. Since the FAA assessed and disclosed the total known costs of the AD requirements in the Costs of Compliance section of the proposed AD, and the commenter did not provide additional cost data for the FAA to consider in its cost analysis, it is not necessary to provide additional information in the AD docket.

The FAA has also considered the AD's impact on small entities and provides the following factual basis for its RFA certification.

The Regulatory Flexibility Act of 1980, Public Law 96-354, 94 Stat. 1164 (5 U.S.C. 601-612), as amended by the Small Business Regulatory Enforcement Fairness Act of 1996 (Pub. L. 104-121, 110 Stat. 857, Mar. 29, 1996) and the Small Business Jobs Act of 2010 (Pub. L. 111-240, 124 Stat. 2504, Sept. 27, 2010), requires Federal agencies to consider the effects of the regulatory action on small business and other small entities and to minimize any significant economic impact. The term “small entities” comprises small businesses and not-for-profit organizations that are independently owned and operated and are not dominant in their fields, and governmental jurisdictions with populations of less than 50,000.

Small Entities to Which This AD Applies

The FAA used the definition of small entities in the RFA for this analysis. The RFA defines small entities as small businesses, small governmental jurisdictions, or small organizations. In 5 U.S.C. 601(3), the RFA defines “small business” to have the same meaning as “small business concern” under section 3 of the Small Business Act. The Small Business Act authorizes the Small Business Administration (SBA) to define “small business” by issuing regulations.

The SBA has established size standards for various types of economic activities, or industries, under the North American Industry Classification System (NAICS). These size standards generally define small businesses based on the number of employees or annual receipts. Note that the SBA definition of a small business applies to the parent company and all affiliates as a single entity.

To identify small entities, the FAA first identified the primary NAICS of the entity or parent company, and then used data from different sources ( e.g., company annual reports, Bureau of Transportation Statistics) to determine whether the entity meets the applicable size standard. This AD affects 25 entities, of which 13 are small entities, 3 are not small entities, and the FAA was unable to obtain sufficient data to categorize the remaining 9 entities. The following table presents the numbers and industries of the 16 known entities affected by this AD:

The following table presents the high-case cost impact of this AD on all 13 small entities. The high-case is defined by the cost of an inspection ($128 per helicopter), which then reveals that a replacement is necessary, costing $2,640. These costs are detailed in the “Costs of Compliance” section of this final rule.

RFA Conclusions

While the FAA has determined that this AD affects a substantial number of small entities, the high-case cost of compliance with this AD relative to each small entity's annual revenue is minimal. In the high-case scenario, the AD's cost as a percentage of annual revenue imposes a cost no greater than 1.24 percent. Therefore, as provided in 5 U.S.C. 605(b), the FAA certifies this AD will not result in a significant economic impact on a substantial number of small entities. The FAA did not change this AD as a result of this comment.

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, a change in the Costs of Compliance section (from 38 helicopters to 34 helicopters and corresponding cost changes), 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 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.

Differences Between This AD and the MCAI

The MCAI requires reporting inspection results to the manufacturer, whereas this AD does not.

Interim Action

The FAA considers that this AD is 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.

Costs of Compliance

The FAA estimates that this AD affects 34 helicopters of U.S. registry. The FAA estimates the following costs to comply with this AD: ( printed page 52235)

The FAA estimates the following costs to do any on-condition actions that would be required based on the results of the inspection. The agency has no way of determining the number of helicopters that might need these on-condition actions:

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.

The Amendment

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

91 FR 52231