Is AD 2021-21-09 a recurring Airworthiness Directive?

Yes — AD 2021-21-09 requires a repetitive inspection. Next-due depends on the aircraft's time in service.

Which aircraft does AD 2021-21-09 apply to?

AD 2021-21-09 applies to Boeing — models 737-600, 737-700, 737-700C, 737-800, 737-900, 737. Serial/part conditions may narrow it to specific aircraft.

Airworthiness Directive 2021-21-09

recurring

Official AD 2021-21-09 · FR doc 2021-24225 · 2021-11-08 · airframe

Airworthiness Directives; The Boeing Company Airplanes

What this AD requires

The FAA is superseding Airworthiness Directive (AD) 2005-05- 18, which applied to certain The Boeing Company Model 737-600, -700, - 700C, -800, and -900 series airplanes. AD 2005-05-18 required repetitive inspections for cracking of the webs of the aft pressure bulkhead at a certain body station, and corrective action if necessary. This AD was prompted by cracking found in that inspection area on airplanes not identified in the applicability of AD 2005-05-18. This AD retains the requirements of AD 2005-05-18, revises the applicability to include additional airplanes, and adds an inspection for existing repairs on the newly added airplanes. The FAA is issuing this AD to address the unsafe condition on these products.

Repetitive inspection. Re-inspect. The next-due date/hours depend on this aircraft’s time in service — a records report computes it from the logbooks.

Which aircraft AD 2021-21-09 applies to

MakesBoeing

Models737-600, 737-700, 737-700C, 737-800, 737-900, 737

As identified in Boeing Alert Service Bulletin 737-53A1251, Revision 2, dated January 20, 2021. Installation of STC ST00830SE does not affect the ability to accomplish the actions required by this AD.

Whether AD 2021-21-09 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 2021-21-09 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.