AD Proposed for MD 369/500 Main Transmission Drive Shaft Coupling

The FAA has proposed to adopt a new airworthiness directive (AD) for certain MD Helicopters, LLC (MDHI) Model 369D, 369E, 369F, 369FF, 369H, and 500N helicopters.  

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. 

Proposed AD Requirements 

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 proposed AD would require accomplishing the actions specified in the service information within 50 hours time-in-service or 6 months after the effective date of the AD, whichever occurs first. 

The Proposed AD can be viewed at docket FAA-2026-4666; comments are due August 17, 2026.