AD 56-27-02
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Hiller Aviation | UH-12 | Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters |
| aircraft | Hiller Aviation | UH-12A | Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters |
| aircraft | Hiller Aviation | UH-12B | Airworthiness Directives; Hiller Models UH-12, UH-12A and UH-12B Helicopters |
Unsafe Condition
Defective welds at the clamp lugs on the four upper lord mount supports of P/N 63100-2 lower frame assembly or modified P/N 63100-2M engine mounts may result in rotor mast tilting and loss of collective pitch control.
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Required Actions
Inspect engine mounts for cadmium plating. If uncoated, remove paint from clamp lugs, inspect for identification stamps (7, 8, or no stamp), and remove from service until lugs are rewelded to CAM 18 standards if stamps are present or missing.
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Compliance Time
as soon as possible but not later than February 28, 1957
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Affected Aircraft
Hiller Models UH-12, UH-12A, and UH-12B helicopters including spares with P/N 63100-2 lower frame assembly or modified P/N 63100-2M engine mounts per Hiller Service Bulletin No. 51
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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