Is AD 2021-20-10 a recurring Airworthiness Directive?

No — AD 2021-20-10 is a one-time directive. Verify it was complied with in the aircraft's records.

Which aircraft does AD 2021-20-10 apply to?

AD 2021-20-10 applies to Leonardo S.P.A. — models AB139, AW139. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 2021-20-10

one-time

Official AD 2021-20-10 · FR doc 2021-22468 · 2021-10-18 · airframe

Airworthiness Directives; Leonardo S.p.a. Helicopters

What this AD requires

The FAA is adopting a new airworthiness directive (AD) for certain Leonardo S.p.a. Model AB139 and AW139 helicopters. This AD was prompted by a report of several occurrences of a cracked main gearbox (MGB) spherical bearing lock nut (lock nut). This AD requires removing from service a certain part-numbered MGB lock nut that is installed on certain part-numbered MGBs and replacing it with newly designed MGB lock nut. This AD also prohibits installing any MGB with the affected MGB lock nut and prohibits installing any affected MGB lock nut on any helicopter. The FAA is issuing this AD to address the unsafe condition on these products.

Which aircraft AD 2021-20-10 applies to

MakesLeonardo S.P.A.

ModelsAB139, AW139

Part-conditional — 3G6320A09152, 3G6320A00131, 3G6320A00132, 3G6320A00133, 3G6320A00134, 3G6320A00135, 3G6320A00136, 3G6320A22031.

Applies only to helicopters WITHOUT main gearbox (MGB) spherical bearing lock nut P/N 3G6320A09152 installed, AND: (1) with MGB P/N 3G6320A00131, 3G6320A00132, 3G6320A00133, 3G6320A00134, 3G6320A00135, 3G6320A00136, 3G6320A22031, 4G6320A00132, or 4G6320A00133 installed; or (2) MGB P/N 3G6320A00133 with 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, or V386, or V622; or (3) MGB P/N 3G6320A00136 with S/N AW1, AW2, AW3, AW5, or AW10. These are main gearbox component serial numbers, not aircraft serials.

Whether AD 2021-20-10 actually applies to your aircraft (by serial and installed parts) and whether it’s already complied with comes from that aircraft’s records.

How AD compliance is recorded

A valid compliance record (14 CFR 43.9) states:

Method of compliance — The specific action taken (inspected, replaced, modified) and to what revision.

Date — When the work was done.

Aircraft time — Total time in service / tach at compliance — how recurring next-due is computed.

Signature & certificate — The A&P/IA who returned it to service, with certificate number.

Is AD 2021-20-10 complied with on your aircraft?

Tailplate reads a tail number’s logbooks and matches every applicable AD — including this one — to its compliance evidence, with recurring next-due dates computed.

Look up a tail number →Read the full directive (Federal Register)

Applicability is derived from the FAA directive corpus and is advisory, not a legal airworthiness determination. Compliance is established only from an aircraft’s actual records.