AD 73-20-03
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12 | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12A | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12B | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12C | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12D | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
| aircraft | Hiller Aviation | Siam Hiller Holdings, Inc. | UH-12E-L | Airworthiness Directives; Hiller Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E Helicopters |
Unsafe Condition
Cracks in the main rotor hub parts numbered 51437, 51437-6, 51437-7, 51437-8, 51437-9, 51437-11, 51437-901, and 51437-11-911 in the area opposite the control rotor trunnion attachments.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Conduct dye penetrant inspection of the main rotor hubs with specified part numbers inside the hub in the area opposite the control rotor trunnion attachments. Replace cracked hubs with new parts before further flight and continue 50-hour interval inspections. Report cracks found including model, serial number, and total time in service to the FAA.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within the next 5 hours time in service after the effective date of this AD, unless already accomplished on receipt of the airmail AD dated September 6, 1973, and thereafter at intervals not to exceed 50 hours time in service from the last inspection
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Hiller Aviation and Siam Hiller Holdings, Inc. Models UH-12, UH-12A, UH-12B, UH-12C, UH-12D, and UH-12E 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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