Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 747-400 and 747-400D series airplanes. This proposed AD would require repetitive inspections to detect cracks in the floor panel attachment fastener holes of the Section 41 upper deck floor beam upper chords, and related investigative and corrective actions if necessary. This proposed AD results from reports of cracks found in the Section 41 upper deck floor beam upper chords. We are proposing this AD to detect and correct cracks in these chords, which could become large and cause the floor beams to become severed and result in rapid decompression or reduced controllability of the airplane.