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

The FAA has issued Airworthiness Directive (AD) 2026-21-05 for certain MD Helicopters, LLC (MDHI) Model 369D, 369E, 369F, 369FF, 369H, and 500N helicopters with a main transmission drive shaft coupling (coupling) part number (P/N) 369H5660, serial numbers 8564-0001 through 8564-0308, installed. The AD is effective November 27, 2026.

Background

The AD was prompted by a report that couplings P/N 369H5660 were found with mechanical damage to the root fillets, spline faces, and the major diameter. A new vendor improperly manufactured 148 of these couplings, which were shipped to customers between June 3, 2020, and May 1, 2022. The manufacturer has recovered 86 of them; the other 62 are at unknown locations. If not addressed, fatigue cracks could grow from the damaged areas and cause the coupling to fail. That would mean loss of power to the main rotor blades and a possible emergency autorotational landing.

AD Requirements

Within 50 hours time-in-service (TIS) or 6 months after the effective date, whichever occurs first, operators must visually inspect each coupling for spline cracks using a bright light and 10X magnification.

• If any cracks are found, the coupling must be replaced before further flight.
• If no cracks are found, the coupling must still be replaced within 300 hours TIS after the effective date.

AD 2026-21-05 can be viewed at docket FAA-2026-4666.