AD 2013-20-51
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | AgustaWestland | S.p.A. (Agusta) | Airworthiness Directives; AgustaWestland S.p.A. (Agusta) Helicopters |
Unsafe Condition
Cracking on Thomas coupling nuts that connect the flexible disc coupling with the splined adapter on the tail rotor drive shaft, resulting from a production deficiency (hydrogen embrittlement).
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Required Actions
Visually inspect each Thomas coupling nut, P/N MS21042L4, along the tail rotor drive shaft line for a crack. If any nut is cracked, replace all nuts with nuts, P/N NAS1805-4, before further flight. Replace all nuts, P/N MS21042L4, with nuts, P/N NAS1805-4, within 10 hours time-in-service (TIS) or 30 days, whichever occurs first. Prohibit installing a Thomas coupling nut, P/N MS21042L4, on any tail rotor drive shaft line.
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Compliance Time
Before further flight for inspection and replacement if cracked; within 10 hours TIS or 30 days for replacement of all nuts, whichever occurs first.
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Affected Aircraft
AgustaWestland S.p.A. (Agusta) Model A109A, A109A II, A109C, A109E, A109K2, A109S, AW109SP, A119, and AW119 MKII helicopters.
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Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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