2026-13365: Airworthiness Directives; MD Helicopters, LLC Helicopters

Federal Register, Volume 91 Issue 125 (Wednesday, July 1, 2026) [Federal Register Volume 91, Number 125 (Wednesday, July 1, 2026)] [Proposed Rules] [Pages 39903-39906] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 2026-13365] ======================================================================= ----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. FAA-2026-4666; Project Identifier AD-2025-01677-R] RIN 2120-AA64 Airworthiness Directives; MD Helicopters, LLC Helicopters

Agency

Federal Aviation Administration (FAA), DOT. [[Page 39904]]

Action

Notice of proposed rulemaking (NPRM). -----------------------------------------------------------------------

Summary

The FAA proposes to adopt a new airworthiness directive (AD) for certain MD Helicopters, LLC (MDHI) Model 369D, 369E, 369F, 369FF, 369H, and 500N helicopters. This proposed AD was prompted by a report of mechanical damage to the main transmission drive shaft coupling (coupling). This proposed AD would require a one-time visual inspection of the couplings for cracks of the splines and, depending on the results, replacement of the couplings. 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 August 17, 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-2026-4666; 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, any comments received, and other information. The street address for Docket Operations is listed above. Material Incorporated by Reference: For MD Helicopters material identified in this proposed AD, contact MDHI, 4555 East McDowell Road, Mesa, AZ 85215-9734; phone: (480) 346-6300; email: [email protected]; website: mdhelicopters.com/contact/. You may view this material at the FAA, Airworthiness Products Section, Operational Safety Branch, 10101 Hillwood Parkway, Fort Worth, TX 76177. For information on the availability of this material at the FAA, call (817) 222-5110.

For Further Information Contact

Binod Singh, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: (562) 627- 5228; 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 ADDRESSES. Include ``Docket No. FAA-2026-4666; Project Identifier AD-2025-01677-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 Binod Singh, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712. 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 received a report that couplings part number (P/N) 369H5660 were found with mechanical damage to the root fillets, spline faces, and the major diameter on Model 369D, 369E, 369F, 369FF, 369H, and 500N helicopters. It was also reported that a new vendor improperly manufactured coupling P/N 369H5660, with a total of 148 shipped to customers between June 3, 2020, and May 1, 2022. The manufacturer reported that 86 affected couplings have been recovered, with the remaining 62 affected couplings at unknown locations. This condition, if not addressed, could result in fatigue cracks that grow from the damaged root fillets and spline faces, which could lead to failure of the coupling with consequent loss of power to the main rotor blades and possible emergency autorotational landing. 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 MD Helicopters Service Bulletin SB369H-264R1 for Model 369H helicopters, SB369D-230R1 for Model 369D helicopters, SB369E-130R1 for Model 369E helicopters, SB369F-121R1 for Model 369F and 369FF helicopters, and SB500N-067R1 for Model 500N helicopters, dated May 26, 2023 (co-published as one document). This material specifies procedures for a one-time visual inspection of the couplings for mechanical damage or cracks of the splines and, if necessary, replacement of the couplings. 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 require accomplishing the actions specified in the service information already described. Costs of Compliance The FAA estimates that this AD, if adopted as proposed, would affect 568 helicopters of U.S. registry. The FAA estimates the following costs to comply with this proposed AD: [[Page 39905]] Estimated Costs ---------------------------------------------------------------------------------------------------------------- Cost per Cost on U.S. Action Labor cost Parts cost product operators ---------------------------------------------------------------------------------------------------------------- Visual inspection of the couplings.... 1 work-hour x $85 per $0 $85 $48,280 hour = $85. ---------------------------------------------------------------------------------------------------------------- The FAA estimates the following costs to do any replacement 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 this replacement: On-Condition Costs ---------------------------------------------------------------------------------------------------------------- Action Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- Replace coupling..................... 2 work-hours x $85 per $1,681 (per coupling).. Up to $3,532. hour = $170. ---------------------------------------------------------------------------------------------------------------- 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 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 0