AD 83-25-02
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12 | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12A | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12B | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12C | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12D | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12L | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12L4 | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E-L | Airworthiness Directives; HILLER AVIATION Models UH-12D, UH-12E, UH12E 4 Place, OH-23G and H-23F, Series Helicopters |
Unsafe Condition
Main rotor blade failure due to delamination of the main rotor blade root doublers or skin bond separation.
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Required Actions
Visually check the main rotor blade root doubler area for delamination before each flight. Inspect for delamination every 50 hours time in service and for skin bond separation every 100 hours time in service. Replace blades with delamination or bond separation and mark rejected blades as 'UNAIRWORTHY'.
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Compliance Time
Prior to further flight after the effective date (December 29, 1983), and before each subsequent flight for visual checks. Inspections must be done within the next 50 hours time in service for delamination and 100 hours time in service for bond separation, with recurring intervals not exceeding those times.
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Affected Aircraft
Hiller Aviation models UH-12D, UH-12E, UH12E 4 Place, OH-23G, and H-23F series helicopters with main rotor blades P/N 53200-03, serial numbers 038 through 286, and those converted to turbine power via STC SH177WE or SK178WE.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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