AD Amdt-39-9417
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Boeing | Defense and Space Group | Airworthiness Directives; Boeing Defense and Space Group Helicopter Division Model 234 Series Helicopters |
Unsafe Condition
Loose nuts on the forward and aft transmission first stage sun and spiral bevel ring gear bolted connection can cause wear of the spiral bevel ring gear flange surface, failure of the bolted connection, transmission failure, and subsequent loss of control of the helicopter.
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Required Actions
Conduct Spectrometric Oil Analysis Program (SOAP) sample inspections, visual inspections of pinion and spiral bevel ring gear teeth for scuffing, and bolt torque inspections of the bolted connection at specified intervals. Replace unairworthy parts and transmissions as required based on inspection results.
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Compliance Time
Within 10 or 50 flight hours after the effective date, depending on helicopter operation intensity, or prior to specified flight hour thresholds.
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Affected Aircraft
Boeing Model 234 series helicopters with forward rotor transmission part numbers 234D1200-2, -3, -4 or aft rotor transmission part numbers 234D2200-3, -4 installed.
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Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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