# Proposed AD FAA-2024-2555: Siam Hiller Holdings, Inc, Helicopters

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 2025-15-02
- Products: Siam Hiller Holdings
- Product type: Aircraft
- Action: Notice of proposed rulemaking (NPRM).
- Published: January 14, 2025, 90 FR 3046
- Comments due: February 28, 2025
- Became: [AD 2025-15-02](https://openairdocs.org/ad/2025-15-02)
- Docket: FAA-2024-2555 (https://www.regulations.gov/docket/FAA-2024-2555, where comments are filed)
- Project: AD-2024-00214-R
- FR document: 2025-00588
- Official PDF: https://openairdocs.org/files/sha256/19/5d/195df31d4f42fb3604d555f99b6715e467489b51a4bf8298f7bab4187c4cc845 (from https://www.govinfo.gov/content/pkg/FR-2025-01-14/pdf/2025-00588.pdf)
- Federal Register: https://www.federalregister.gov/documents/2025/01/14/2025-00588/airworthiness-directives-siam-hiller-holdings-inc-helicopters
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/FR-ADNPRM-2025-00588-00000000000.0001
- Page: https://openairdocs.org/proposed/FAA-2024-2555

## Summary

The FAA proposes to adopt a new airworthiness directive (AD) for Siam Hiller Holdings, Inc. (Siam Hiller), Model UH-12E (Army OH-23G and H-23F) and UH-12E-L helicopters. This proposed AD was prompted by reports of cracks found in a main rotor (M/R) transmission drive shaft (drive shaft). This proposed AD would require inspecting certain M/R drive shafts for a crack, prohibit installing certain M/R drive shafts unless the inspection is done, and prohibit using certain paint removers. The FAA is proposing this AD to address the unsafe condition on these products.

## Notices in this docket

- Jan 14, 2025: Notice of proposed rulemaking (NPRM). (first notice), FR document 2025-00588, comments due Feb 28, 2025 (https://www.federalregister.gov/documents/2025/01/14/2025-00588/airworthiness-directives-siam-hiller-holdings-inc-helicopters)

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