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

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.