2026-21-05: Engine/transmission coupling

1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. 2. The FAA amends § 39.13 by adding the following new airworthiness directive: 2026-21-05 MD Helicopters, LLC: Amendment 39-23494; Docket No. FAA-2026-4666; Project Identifier AD-2025-01677-R. (a) Effective Date This airworthiness directive (AD) is effective November 27, 2026. (b) Affected ADs None. (c) Applicability This AD applies to MD Helicopters, LLC (MDHI) Model 369D, 369E, 369F, 369FF, 369H, and 500N helicopters, certificated in any category, with an installed main transmission drive shaft coupling (coupling) part number 369H5660 with serial numbers 8564-0001 through 8564-0308. (d) Subject Joint Aircraft System Component (JASC) Code 6310, Engine/transmission coupling. (e) Unsafe Condition This AD was prompted by a report of mechanical damage to the coupling. The FAA is issuing this AD to detect and address couplings with damage to the root fillets, spline faces, and major diameter. The unsafe 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. (f) Compliance Comply with this AD within the compliance times specified, unless already done. (g) Required Actions Within 50 hours time-in-service (TIS) or 6 months after the effective date of this AD, whichever occurs first, using a bright light and 10X magnification, visually inspect each coupling for cracks to the spline. Note 1 to paragraph (g): Examples of acceptable couplings with standard broaching tool marks and mechanical damage may be found in Figure 1 and Figure 2, as applicable, of MD Helicopters Service Bulletin SB369H-264R1, SB369D-230R1, SB369E-130R1, SB369F-121R1, and SB500N-067R1, dated May 26, 2023 (co-published as one document). (1) If any cracks are found on any coupling, before further flight, remove the affected coupling from service and replace with a serviceable coupling. (2) If there are no cracks on any coupling, within 300 hours TIS after the effective date of this AD, replace the affected coupling with a serviceable coupling. (h) Alternative Methods of Compliance (AMOCs) (1) The Manager, West Certification 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 West Certification Branch, send it to the attention of the person identified in paragraph (i) 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. (i) Additional Information For more information about this AD, contact Binod Singh, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: (562) 627-5228; email: [email protected] . (j) Material Incorporated by Reference None. Issued on October 20, 2026. Steven W. Thompson, Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service. [FR Doc. 2026-21664 Filed 10-22-26; 8:45 am]BILLING CODE 4910-13-P