AD 99-23-23
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Bell Helicopter Textron, Inc. | 412 | Airworthiness Directives; Bell Helicopter Textron, Inc. Model 412, 412EP and 412CF Helicopters |
| aircraft | Bell Helicopter Textron, Inc. | 412CF | Airworthiness Directives; Bell Helicopter Textron, Inc. Model 412, 412EP and 412CF Helicopters |
| aircraft | Bell Helicopter Textron, Inc. | 412EP | Airworthiness Directives; Bell Helicopter Textron, Inc. Model 412, 412EP and 412CF Helicopters |
Unsafe Condition
Fatigue failure of the main rotor yoke assembly (yoke) due to manufacturing below 0.478-inch thickness, leading to loss of a main rotor blade and subsequent loss of control of the helicopter.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Inspect and measure the thickness of main rotor yoke assemblies (part numbers 412-010-101-123 or -127). For yokes measuring less than 0.478-inch thickness, add 500 hours time-in-service (TIS) to the component's total time and document the measurement and added hours on the component history card or equivalent record.
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Compliance Time
Within 10 hours time-in-service for yokes with 4,500+ hours TIS, or within 90 days for yokes with less than 4,500 hours TIS but before reaching 4,500 hours TIS.
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Affected Aircraft
Bell Model 412/412EP (S/N 33001-33213, 34001-34036, 36001-36204) and 412CF (S/N 46400-46499) helicopters with main rotor yoke assemblies P/N 412-010-101-123/-127 installed.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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