# [Amended]
**AGENCY:**
Federal Aviation Administration (FAA), DOT.
**ACTION:**
Notice of proposed rulemaking (NPRM).
**SUMMARY:**
The FAA proposes to supersede Airworthiness Directive (AD) 2025-06-04, which applies to all Airbus Helicopters Model AS350B, AS350B1, AS350B2, AS350B3, AS350BA, AS350D, AS355E, AS355F, AS355F1, AS355F2, AS355N, AS355NP, EC130B4, and EC130T2 helicopters. AD 2025-06-04 requires repetitively inspecting the main gearbox (MGB) bevel wheel and the MGB magnetic plug for particles and performing corrective actions if applicable and prohibits installing an affected MGB unless certain requirements are met. Since the FAA issued AD 2025-06-04, the FAA determined that AD 2025-06-04 contains errors in the interval compliance times. This proposed AD would continue to require the actions of AD 2025-06-04 and revise the interval compliance times. The FAA is proposing this AD to address the unsafe condition on these products.
**DATES:**
The FAA must receive comments on this proposed AD by January 9, 2026.
**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-2025-5032; 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.
**FOR FURTHER INFORMATION CONTACT:**
Dan McCully, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (404) 474-5548; 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-2025-5032; Project Identifier AD-2025-01042-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 revise 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 Dan McCully, 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 FAA issued AD 2025-06-04, Amendment 39-22992 (90 FR 14723, April 4, 2025) (AD 2025-06-04), for all Airbus Helicopters Model AS350B, AS350B1, AS350B2, AS350B3, AS350BA, AS350D, AS355E, AS355F, AS355F1, AS355F2, AS355N, AS355NP, EC130B4, and EC130T2 helicopters. AD 2025-06-04 was prompted by EASA AD 2023-0044, dated February 28, 2023 (EASA AD 2023-0044) (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 that after a fleet design review for detection of particles in the MGB, it was determined that additional maintenance actions are necessary to improve detection of particles in MGB that have certain part-numbered planet gear bearings installed. AD 2025-06-04 requires repetitively inspecting the MGB bevel wheel and the MGB magnetic plug for the presence of particles, close monitoring of the MGB magnetic plug if particles are detected, and replacing the epicyclic module if necessary. The AD also prohibits installing an affected MGB unless certain requirements are met. The agency issued AD 2025-06-04 to detect and correct the presence of particles in the MGB which, if not addressed, could result in reduced or loss of control of the helicopter.
**Actions Since AD 2025-06-04 Was Issued**
Since the FAA issued AD 2025-06-04, the FAA determined that there are errors in the interval compliance times in Table 1 to paragraph (h)(6)(i) of AD 2025-06-04. Airbus Helicopters Model AS350B, AS350B1, AS350BA, AS350D, AS355E, AS355F, AS355F1, AS355F2, AS355N, and AS355NP helicopters should have an interval compliance time of 100 hours time-in-service (TIS) instead of 30 hours TIS. Also, Airbus Helicopters Model EC130B4 helicopters should have an interval compliance time of 100 hours TIS instead of 150 hours TIS.
**FAA's Determination**
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.
**Material Incorporated by Reference Under 1 CFR Part 51**
The FAA reviewed EASA AD 2023-0044, which specifies procedures for repetitive borescope visual inspections of the bevel wheel of the affected MGB for particles, collecting and analyzing any particles detected, and depending on the results, accomplishing further actions, accomplishing corrective action in accordance with the ASB, or contacting AH [Airbus Helicopters] for further corrective action. EASA AD 2023-0044 also specifies procedures for accomplishing a borescope visual inspection of the bevel wheel of the affected MGB for particles following the detection of any particles at the MGB magnetic plug during accomplishment of certain maintenance tasks and depending on the results, taking corrective action. EASA AD 2023-0044 also prohibits installing an affected MGB on any helicopter unless certain requirements are met.
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.
**Proposed AD Requirements in This NPRM**
This proposed AD would continue to require the actions of AD 2025-06-04, except that this proposed AD would revise the interval compliance times. The actions proposed in this AD are specified in EASA AD 2023-0044, 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 applies to Model AS350BB helicopters, whereas this proposed AD would not because that model does not have an FAA type certificate.
Where Note 1 in the material referenced in the MCAI specifies the option of 1 mechanical technician and 1 crew member, for this proposed AD, the pilot is only permitted to turn the tail rotor (b) because the other actions specified in the note must be accomplished by persons authorized under 14 CFR 43.3. Therefore, for the purposes of this proposed AD, the owner/operator (pilot) may turn the tail rotor (b) and must enter compliance with the applicable paragraph of this proposed AD in the helicopter 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 turning the tail rotor (b). This action can be performed equally well by a pilot or a mechanic. This action is an exception to the FAA's standard maintenance regulations.
This proposed AD would not require complying with paragraph (2) of the MCAI. Instead, this proposed AD would require repetitively inspecting the MGB magnetic plug for particles and, if there is any particle, accomplishing a borescope visual inspection, as specified in paragraphs (h)(6)(i) and (ii) of this proposed AD.
Where the material referenced in the MCAI specifies contacting Airbus Helicopters for a certain action, this proposed AD would require accomplishing action in accordance with a method approved by the FAA, EASA, or Airbus Helicopters' EASA Design Organization Approval.
**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 2023-0044 by reference in the FAA final rule. This proposed AD would, therefore, require compliance with EASA AD 2023-0044 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 2023-0044 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 2023-0044. Material required by EASA AD 2023-0044 for compliance will be available at *www.regulations.gov* by searching for and locating Docket No. FAA-2025-5032 after the FAA final rule is published.
**Costs of Compliance**
The FAA estimates that this AD, if adopted as proposed, would affect 522 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. |
| --- | --- | --- | --- | --- |
| Visually inspect MGB bevel wheel | 1 work-hour × $85 per hour = $85 | $0 | $85 | $44,370 |
| Repetitively inspect magnetic plugs of the MGB | 1 work-hour × $85 per hour = $85 | 0 | 85 | 44,370 |
The new requirements of this proposed AD add no additional economic burden.
The FAA estimates the following costs to do any on-condition actions that would be required based on the results of the proposed inspections. 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 product |
| --- | --- | --- | --- |
| Collect particles and perform metallurgical analysis | 6 work-hours × $85 per hour = $510 | $0 | $510. |
| Close monitoring | 2 work-hours × $85 per hour = $170 | $0 | $170 per close monitoring cycle. |
| Perform visual borescope inspection of MGB bevel wheel | 1 work-hour × $85 per hour = $85 | $0 | $85. |
| Replace epicyclic module | 56 work-hours × $85 per hour = $4,760 | $50,524 (overhauled) | $55,284 per module. |
| Replace bevel reduction module | 56 work-hours × $85 per hour = $4,760 | $18,500 (overhauled) | $23,260 per module. |
Certain corrective action could vary significantly from helicopter to helicopter. The FAA has no data to determine the costs to accomplish the corrective action.
**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 2025-06-04, Amendment 39-22992 (90 FR 14723, April 4, 2025); and
b. Adding the following new airworthiness directive:
*Airbus Helicopters:* Docket No. FAA-2025-5032; Project Identifier AD-2025-01042-R.
**(a) Comments Due Date**
The FAA must receive comments on this airworthiness directive (AD) by January 9, 2026.
**(b) Affected ADs**
This AD replaces AD 2025-06-04, Amendment 39-22992 (90 FR 14723, April 4, 2025) (AD 2025-06-04).
**(c) Applicability**
This AD applies to all Airbus Helicopters Model AS350B, AS350B1, AS350B2, AS350B3, AS350BA, AS350D, AS355E, AS355F, AS355F1, AS355F2, AS355N, AS355NP, EC130B4, and EC130T2 helicopters, certificated in any category.
**(d) Subject**
Joint Aircraft System Component (JASC) Code 6320, Main Rotor Gearbox.
**(e) Unsafe Condition**
This AD was prompted by an assessment performed by the manufacturer which determined that additional maintenance actions are necessary to improve detection of particles in the main gearbox (MGB) with certain part-numbered planet gear bearings installed. The FAA is issuing this AD to detect and correct particles in the MGB. The unsafe condition, if not addressed, could result in reduced or loss of control of the helicopter.
**(f) Compliance**
Comply with this AD within the compliance times specified, unless already done.
**(g) Required Actions**
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 2023-0044, dated February 28, 2023 (EASA AD 2023-0044).
**(h) Exceptions to EASA AD 2023-0044**
(1) Where EASA AD 2023-0044 defines “serviceable MGB” as “An affected MGB which has accumulated less than 330 flight hours (FH) since new (first installation on a helicopter), or since an overhaul, or since an inspection in accordance with the instructions of the ASB”, this AD requires replacing that text with “An affected MGB which has accumulated less than 330 total hours time-in-service (TIS) since new (zero total hours TIS), since last overhaul if an overhaul has been accomplished, or since last inspection and any specified corrective action in accordance with the instructions of the ASB if an inspection and any specified corrective action by following the instructions of the ASB have been accomplished”.
(2) Where EASA AD 2023-0044 requires compliance in terms of flight hours, this AD requires using TIS.
(3) Where EASA AD 2023-0044 refers to its effective date, this AD requires using May 9, 2025 (the effective date of AD 2025-06-04).
(4) Where Note 1 in the material referenced in paragraph (1) of EASA AD 2023-0044 specifies the option of 1 mechanical technician and 1 crew member, for this AD, the pilot is only permitted to turn the tail rotor (b). The owner/operator (pilot) holding at least a private pilot certificate may turn the tail rotor (b) and must enter compliance with paragraph (g) of this AD in the helicopter 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, 121.380, or 135.43. All other actions specified in Note 1 in the material referenced in paragraph (1) of EASA AD 2023-0044 must be accomplished by persons authorized under 14 CFR 43.3.
(5) Where Note 2 in the material referenced in paragraph (1) of EASA AD 2023-0044 specifies contacting Airbus Helicopters [AH] for further instructions if the bottom of the radius (a6) of the bevel wheel (a3) or head screws (a4) (see Figure 2) are not clearly visible, this AD requires, before further flight, accomplishing action in accordance with a 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.
(6) Instead of complying with paragraph (2) of EASA AD 2023-0044, comply with the actions required by paragraphs (h)(6)(i) and (ii) of this AD.
(i) After May 9, 2025 (the effective date of AD 2025-06-04), and within the compliance time intervals specified in table 1 to paragraph (h)(6)(i) of this AD, visually inspect the MGB magnetic plug for particles.
*Note 1 to paragraph (h)(6)(i):* Aircraft Maintenance Manual (AMM) task 60-00-00, 6-2A, or AMM task 60-00-00, 6-2, or Work Card 60-00-00-602, as applicable, provides information regarding inspecting the MGB magnetic plug.
| Helicopter model(s) | Initial compliance times | Interval compliance times |
| --- | --- | --- |
| AS350B, AS350B1, AS350BA, and AS350D | 5 | 100 |
| AS355E, AS355F, AS355F1, AS355F2, AS355N, and AS355NP | 5 | 100 |
| AS350B2 and AS350B3 | 10 | 100 |
| EC130B4 | 5 | 100 |
| EC130T2 | 5 | 150 |
(ii) If there is any particle as a result of any MGB magnetic plug inspection required by paragraph (h)(6)(i) of this AD, before further flight, borescope inspect the bevel wheel of the affected MGB for particles as required by paragraph (1) of EASA AD 2023-0044. If there is any particle as a result of the borescope inspection of the bevel wheel, before further flight, collect and analyze the particles as required by paragraph (3) of EASA AD 2023-0044.
(7) Where paragraph (3) of EASA AD 2023-0044 specifies “If, during any inspection as required by paragraph (1) or (2) of this AD”, this AD requires replacing that text with “If, during any inspection as required by paragraph (1) of this AD”.
(8) Where the material referenced in paragraph (3) of EASA AD 2023-0044 specifies performing a metallurgical analysis and contacting Airbus Helicopters if collected particles cannot be characterized with Work Card 20-08-01-601, this AD does not require contacting Airbus Helicopter but does require performing the metallurgical analysis.
(9) Where the material referenced in paragraph (3) of EASA AD 2023-0044 contains a special flight permit provision, this AD does not allow that provision but instead requires the special flight permit limitations in paragraph (j) of this AD.
(10) Where the material referenced in paragraph (3) of EASA AD 2023-0044 specifies contacting Airbus Helicopters if the damaged module cannot be identified, this AD requires, before further flight, accomplishing action in accordance with a method approved by the FAA, EASA, or Airbus Helicopters' EASA DOA. If approved by the DOA, the approval must include the DOA-authorized signature.
(11) Where paragraph (5) of EASA AD 2023-0044 states “to contact AH for corrective action(s) instructions, and within the compliance time specified therein, to accomplish those instructions accordingly”, this AD requires replacing that text with “accomplishing corrective actions in accordance with a method approved by the FAA, EASA, or Airbus Helicopters' EASA DOA. If approved by the DOA, the approval must include the DOA-authorized signature”.
(12) Where paragraph (7) of EASA AD 2023-0044 states “since new (first installation a helicopter), or since an overhaul, or since an inspection in accordance with the instructions of the ASB, as applicable, and, thereafter, as required by this AD”, this AD requires replacing that text with “since new (zero total hours time-in-service), or since last overhaul if an overhaul has been accomplished, or since last inspection and any specified corrective action in accordance with the instructions of the ASB if an inspection and any specified corrective action by following the instructions of the ASB have been accomplished, and thereafter as required by this AD”.
(13) This AD does not adopt the “Remarks” section of EASA AD 2023-0044.
**(i) No Reporting Requirement**
Although the material referenced in EASA AD 2023-0044 specifies to submit certain information to the manufacturer, this AD does not require that action.
**(j) Special Flight Permit**
A special flight permit may be issued in accordance with 14 CFR 21.197 and 21.199 to permit a one-time, non-revenue flight to a location where the actions required by this AD can be accomplished. This flight must be performed with only essential flight crew.
**(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 Dan McCully, Aviation Safety Engineer, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; phone: (404) 474-5548; 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.
(3) The following material was approved for IBR on May 9, 2025 (90 FR 14723; April 4, 2025).
(i) European Union Aviation Safety Agency (EASA) AD 2023-0044, dated February 28, 2023.
(ii) [Reserved]
(4) 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.*
(5) 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.
(6) 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 November 20, 2025.
Steven W. Thompson,
Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.