# Proposed AD FAA-2026-4666: MD Helicopters, LLC Helicopters

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 2026-21-05
- Products: MD Helicopters 369D, 369E, 369F, 369FF, 369H and 500N
- Product type: Aircraft
- Action: Notice of proposed rulemaking (NPRM).
- Published: July 1, 2026, 91 FR 39903
- Comments due: August 17, 2026
- Became: [AD 2026-21-05](https://openairdocs.org/ad/2026-21-05)
- Docket: FAA-2026-4666 (https://www.regulations.gov/docket/FAA-2026-4666, where comments are filed)
- Project: AD-2025-01677-R
- FR document: 2026-13365
- Official PDF: https://openairdocs.org/files/sha256/ae/37/ae376c61f4ab3e542ec00baa982c8580f9065f13399bfc0c7d5109f120ad00bb (from https://www.govinfo.gov/content/pkg/FR-2026-07-01/pdf/2026-13365.pdf)
- Federal Register: https://www.federalregister.gov/documents/2026/07/01/2026-13365/airworthiness-directives-md-helicopters-llc-helicopters
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/FR-ADNPRM-2026-13365-00000000000.0001
- Page: https://openairdocs.org/proposed/FAA-2026-4666

## 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.

## Notices in this docket

- Jul 1, 2026: Notice of proposed rulemaking (NPRM). (first notice), FR document 2026-13365, comments due Aug 17, 2026 (https://www.federalregister.gov/documents/2026/07/01/2026-13365/airworthiness-directives-md-helicopters-llc-helicopters)

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