FAA · Airworthiness Directive
Airworthiness Directives; Siam Hiller Holdings, Inc.
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.
Applicability
Aircraft makes and models this AD applies to, sorted by US-registered fleet size.
Federal Register text
Verbatim from the Federal Register publication — required actions, compliance times, parts/serial numbers, and methods of compliance. The Federal Register is the legally binding document; this rendering is for readability. Cite: 90 FR 40529.
[Federal Register Volume 90, Number 159 (Wednesday, August 20, 2025)] [Rules and Regulations] [Pages 40529-40531] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 2025-15839]
======================================================================== Rules and Regulations Federal Register ________________________________________________________________________ This section of the FEDERAL REGISTER contains regulatory documents having general applicability and legal effect, most of which are keyed to and codified in the Code of Federal Regulations, which is published under 50 titles pursuant to 44 U.S.C. 1510. The Code of Federal Regulations is sold by the Superintendent of Documents. ========================================================================
Federal Register / Vol. 90, No. 159 / Wednesday, August 20, 2025 / Rules and Regulations
[[Page 40529]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2024-2555; Project Identifier AD-2024-00214-R; Amendment 39-23089; AD 2025-15-02] RIN 2120-AA64
Airworthiness Directives; Siam Hiller Holdings, Inc.
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
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SUMMARY: 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.
DATES: This AD is effective September 24, 2025.