Action
Final rule.
Summary
We are superseding Airworthiness Directive (AD) 2009-10-06 for certain The Boeing Company Model 747-400 and -400D series airplanes. AD 2009-10-06 required repetitive inspections to detect cracks in the floor panel attachment fastener holes of the Section 41 upper deck floor beam upper chords, and corrective actions if necessary; and repetitive post-repair and post-modification inspections, and corrective actions if necessary. This new AD adds repetitive inspections of Section 44 upper deck floor beam upper chords, and corrective actions if necessary; repetitive post-repair and post- modification inspections, and corrective actions if necessary; and replacement of the upper deck floor beam upper chords. This AD was prompted by an evaluation by the design approval holder (DAH) indicating that certain upper chords of the upper deck floor beam are subject to widespread fatigue damage (WFD). We are issuing this AD to detect and correct fatigue cracking in certain upper chords of the upper deck floor beam, which could become large and cause the floor beams to become severed and result in rapid decompression or reduced controllability of the airplane.