AD 74-04-03
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12D | Airworthiness Directives; Hiller Models UH-12D and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E | Airworthiness Directives; Hiller Models UH-12D and UH-12E Helicopters |
Unsafe Condition
Main rotor drag struts P/N 52120 may have unacceptably low heat-treat condition leading to premature fatigue failure.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Inspect main rotor drag struts P/N 52120 per Hiller Service Bulletin 51-2, check Rockwell hardness using 'C' scale, replace struts with Rockwell 'C' less than 23 within 50 hours or 2500 hours, replace struts with Rockwell 'C' 23-31 within 50 hours or 1200 hours but not exceeding 2500 hours, repaint and reinstall, or replace with P/N 52120-5.
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Compliance Time
within the next 50 hours' time in service after the effective date of this AD
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Affected Aircraft
Hiller Models UH-12D (H-23D) and UH-12E (3 and 4 place), (OH-23G, H-23F) helicopters certificated in all categories.
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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