# Airworthiness Directives; Siam Hiller Holdings, Inc.
> **Rule** · Final rule. · Published 2025-08-20 · Effective 2025-09-24 · 90 FR 40529
## Document
- **Document number:** 2025-15839
- **Category:** airworthiness
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 90 FR 40529
- **Publication date:** 2025-08-20
- **Effective date:** 2025-09-24
- **FAA docket:** Docket No. FAA-2024-2555
## Abstract

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

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2025/08/20/2025-15839/airworthiness-directives-siam-hiller-holdings-inc)
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