# 2025-00588: Korean War Era Helicopters Still Flying, Now With Cracking Parts

2025-00588, Airworthiness Directives; Siam Hiller Holdings, Inc, Helicopters, is a Federal Register proposed rule from an unnamed agency published 2025-01-14, effective The FAA must receive comments on this proposed AD by February 28, 2025. (as of 2026-06-11).

- Canonical: https://policyrisk.com/federal-register/2025-00588
- As of: 2026-06-11
- Plain-text twin of the page above; the HTML and this file carry the same facts.

## Facts
- Document number: 2025-00588
- Title: Airworthiness Directives; Siam Hiller Holdings, Inc, Helicopters
- Type: Proposed Rule
- Agencies: unknown
- Citation: unknown
- Published: 2025-01-14
- Effective: The FAA must receive comments on this proposed AD by February 28, 2025.
- Comments close: not stated
- Significant: no
- Touches household money: no
- Regulation identifier numbers: none
- Last updated: 2026-06-11

## In one line

Korean War Era Helicopters Still Flying, Now With Cracking Parts

## Summary

If you own or work with Siam Hiller UH-12E helicopters, listen up! The FAA wants you to check the main rotor drive shafts for cracks and stop using certain paint removers to keep your choppers safe. You’ve got until February 28, 2025, to share your thoughts, and these changes could save you from costly repairs down the road.

## Abstract

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.

## Effects PRIA read

- Mandatory drive-shaft inspections and bake: cost, high. If you own or operate a Siam Hiller UH-12E or UH-12E-L with a main rotor drive shaft P/N 23600, you must inspect that drive shaft when it has 1,200 or more hours time-in-service (TIS), or is 4 or more years since new, or at the next overhaul after the AD's effective date. With the shaft removed you…
- Installation and paint-stripper limits: cost, low. As of the effective date of this AD, you may not install a main rotor drive shaft P/N 23600 on any helicopter unless the required removal, bake, and magnetic particle inspection have been completed. Also, you may not use any paint stripper other than TT-R-248B or TT-R-2918A Type I to remove coating…
- Certified NDT inspector required: cost, low. The magnetic particle inspection of the M/R drive shaft must be done by a Level II or Level III inspector certified to FAA-acceptable nondestructive inspection standards (examples in Advisory Circular 65-31B). That means you must use qualified NDT personnel to perform the inspection required by thi…

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## Sources
- [2025-00588 on federalregister.gov](https://www.federalregister.gov/documents/2025/01/14/2025-00588/airworthiness-directives-siam-hiller-holdings-inc-helicopters)
- [2025-00588 as published (PDF)](https://www.govinfo.gov/content/pkg/FR-2025-01-14/pdf/2025-00588.pdf)

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Source: PRIA, https://policyrisk.com/federal-register/2025-00588 (as of 2026-06-11).