Is AD 04-27521 a recurring Airworthiness Directive?

No — AD 04-27521 is a one-time directive. Verify it was complied with in the aircraft's records.

Which aircraft does AD 04-27521 apply to?

AD 04-27521 applies to Great Lakes — models 2T-1A-1, 2T-1A-2. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 04-27521

one-time

AD 04-27521 · 2004-12-16 · airframe

Airworthiness Directives; Great Lakes Aircraft Company, LLC, Models 2T-1A-1 and 2T-1A-2 Airplanes

What this AD requires

The FAA supersedes Airworthiness Directive (AD) 79-20-08, which applies to all Great Lakes Aircraft Company, LLC, (Great Lakes) Models 2T-1A-1 and 2T-1A-2 airplanes with a Lycoming IO-360-B1F6 or AIO-360-B1G6 engine installed. AD 79-20-08 currently requires you to inspect the engine induction system and the alternate air door for any signs of damage and repairing or replacing any damaged components. AD 79-20-08 also requires you to inspect the induction system for the presence of a drain fitting. If the drain fitting is blocked, restricted, or does not exist, AD 79-20-08 requires you to clear the fitting or drill a hole in the elbow at the fitting location. This AD is the result of the FAA inadvertently omitting Lycoming engine AEIO- 360-B1G6 from the applicability section of AD 79-20-08. Consequently, this AD retains the actions required in AD 79-20-08 and adds Lycoming engine AEIO-360-B1G6 to the applicability section. We are issuing this AD to prevent the aircraft induction system from becoming blocked or restricted, which could result in engine failure. This failure could lead to loss of control of the airplane.

Which aircraft AD 04-27521 applies to

MakesGreat Lakes

Models2T-1A-1, 2T-1A-2

applicability derived from the AD summary — confirm the model/serial from the records

Whether AD 04-27521 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 04-27521 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.