AD 51-29-01
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Scotts-Bell 47 Inc | 47B | Airworthiness Directives; Bell Model 47B, 47B3, 47D, 47D1 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47B3 | Airworthiness Directives; Bell Model 47B, 47B3, 47D, 47D1 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47D | Airworthiness Directives; Bell Model 47B, 47B3, 47D, 47D1 Helicopters |
| aircraft | Scotts-Bell 47 Inc | 47D1 | Airworthiness Directives; Bell Model 47B, 47B3, 47D, 47D1 Helicopters |
Unsafe Condition
Tail rotor gearbox shaft (P/N 47-645-028-1 or 47-645-051-1) may develop cracks or elongation in the attachment bolt hole after accumulating 900 hours of operation, leading to tail rotor failure.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Replace the tail rotor gearbox shaft when it has accumulated 900 hours of operation. For shafts already over 900 hours, replace by February 1, 1952. Until then, inspect the attachment bolt hole after every 25 hours of operation for cracks or elongation over 0.010 inch and replace the shaft if found.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Replace by February 1, 1952 for shafts over 900 hours. Inspections required after every 25 hours of operation until replacement.
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Bell Model 47B, 47B3, 47D, 47D1 helicopters
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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