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Airworthiness Directive 98-21-17

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Official AD 98-21-17 · FR doc 98-26966 · 1998-10-13 · airframe

Airworthiness Directives; Boeing Model 747 Series Airplanes Equipped with Pratt & Whitney Model JT9D-70 Engines

What this AD requires

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires repetitive inspections to detect fatigue cracking of the spring beams on the outboard struts; replacement of cracked spring beams with new or serviceable spring beams; and follow-on actions. That action also provides an optional terminating action for the repetitive inspections. This amendment removes that optional terminating action, and requires a new terminating action. This amendment is prompted by the development of an improved process for manufacturing titanium spring beams that will eliminate the embedded porosity flaws in the existing spring beams from which fatigue cracking can originate. The actions specified by this AD are intended to prevent fatigue cracking of the spring beam, which could result in loss of an outboard strut.

Repetitive inspection. Re-inspect every 18 months. The next-due date/hours depend on this aircraft’s time in service — a records report computes it from the logbooks.

Which aircraft AD 98-21-17 applies to

MakesBoeing
Models747

Applies to airplanes identified in the preceding applicability provision regardless of prior modification/repair; requires inspection of outboard strut spring beams for fatigue cracking per Boeing Alert Service Bulletin 747-54A2171 (dated Oct 31, 1994, or Rev 1 dated Jun 27, 1996), with follow-on actions depending on whether terminating action per AD 94-25-01 or titanium spring beam installation has already been accomplished.

Whether AD 98-21-17 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 98-21-17 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.