AD 77-21-01
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Scotts-Bell 47 Inc | 47 | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47B | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47B3 | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47D | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47D1 | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47E | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47G | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47G-2 | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47G-2A | Airworthiness Directives; Bell Model 47 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47G-2A-1 | Airworthiness Directives; Bell Model 47 Helicopters |
Unsafe Condition
Failure of the bearing, part number 47-620-629-3 or 47-620-629-5, or failure of the input pinion shaft, part number 47-645-205-3, located in the tail rotor gear box, part number 47-640-075-1 or 47-640-075-7.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Conduct inspections and replacement activities prescribed by paragraphs 1, 2, 2a, 2b, 3, and 4 of Bell Helicopter Textron Service Bulletin No. 47-77-1, dated February 14, 1977, or later FAA approved revision. Reassemble and reinstall the tail rotor gear box in accordance with Maintenance and Overhaul Instructions for the applicable model helicopters.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within the next 100 hours time in service after the effective date of this Airworthiness Directive, unless already accomplished
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Affected Aircraft
Bell Model 47 helicopters with tail rotor gear boxes, part number 47-640-075-1 or 47-640-075-5 installed. Retrofit kits delivered after December 1, 1976, are exempt.
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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