AD 2021-20-10
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Leonardo | S.p.a. | Airworthiness Directives; Leonardo S.p.a. Helicopters |
Unsafe Condition
A cracked main gearbox (MGB) spherical bearing lock nut (lock nut) has been reported, which could lead to failure of the MGB planetary gears, resulting in loss of control of the helicopter.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Remove from service a certain part-numbered MGB lock nut and replace it with a newly designed MGB lock nut. Prohibit installing any MGB with the affected MGB lock nut and prohibit installing any affected MGB lock nut on any helicopter.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Within 100 hours time in service (TIS) or during the next scheduled MGB overhaul, whichever occurs first after the effective date of this AD.
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Leonardo S.p.a. Model AB139 and AW139 helicopters without MGB lock nut part number (P/N) 3G6320A09152 installed and with MGB P/N 3G6320A00131, 3G6320A00132, 3G6320A00133, 3G6320A00134, 3G6320A00135, 3G6320A00136, 3G6320A22031, 4G6320A00132, or 4G6320A00133 installed; or MGB P/N 3G320A00133 with serial number (S/N) M23, or MGB P/N 3G6320A00134, with S/N M6, N76, N92, P124, P129, P131, P162, P184, Q230, Q243, Q249, R272, V21, V39, V96, V163, V211, V241, V272, V281, V384, V386, or V622 installed; or MGB P/N 3G6320A00136 with S/N AW1, AW2, AW3, AW5, or AW10 installed.
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 6, 2026
Rights: U.S. Government Public Domain
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