Is AD 2013-20-51 a recurring Airworthiness Directive?

No — AD 2013-20-51 is a one-time directive. Verify it was complied with in the aircraft's records.

Which aircraft does AD 2013-20-51 apply to?

AD 2013-20-51 applies to Agusta — models A109A, A109A II, A109C, A109E, A109S, A109K2, AW109SP, A119. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 2013-20-51

one-time

Official AD 2013-20-51 · FR doc 2013-24937 · 2013-10-25 · airframe

Airworthiness Directives; AgustaWestland S.p.A. (Agusta) Helicopters

What this AD requires

We are adopting a new airworthiness directive (AD) for Agusta Model A109A, A109A II, A109C, A109E, A109K2, A109S, AW109SP, A119, and AW119 MKII helicopters. The emergency AD was sent previously to all known U.S. owners and operators of these helicopters. This AD requires, before further flight, inspecting certain Thomas coupling nuts on the tail rotor drive shaft line for a crack and replacing all the nuts if any nut is cracked. Also this AD requires replacing all affected Thomas coupling nuts within 10 hours time-in-service (TIS) or 30 days, whichever occurs first. This AD was prompted by two incidents of cracking on the nuts that connect the flexible disc coupling (Thomas coupling) with the splined adapter on the tail rotor drive shaft. We are issuing this AD to correct the unsafe condition on these helicopters.

Which aircraft AD 2013-20-51 applies to

MakesAgusta

ModelsA109A, A109A II, A109C, A109E, A109S, A109K2, AW109SP, A119, AW119 MKII, A109, AW109, AW119

Part-conditional — MS21042L4.

Applies only to helicopters with tail rotor drive shaft flexible disc coupling (Thomas coupling) nut P/N MS21042L4 installed.

Whether AD 2013-20-51 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 2013-20-51 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.