Airworthiness Directives; Boeing Model 747-400 Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747-400 series airplanes. This AD requires repetitive inspections for any crack in the upper deck floor beam at station 400, which include inspecting the floor beam web and chords, certain fastener holes at the intersection of the floor beam and frame on both sides of the airplane, and certain floor panel attachment fastener holes at the floor beam upper chords. This AD also requires corrective action if necessary. This AD results from several reports indicating that fatigue cracking was found in upper deck floor beams made from 7000 series aluminum alloy. We are issuing this AD to detect and correct cracking in the upper deck floor beam at station 400, which could extend and sever the floor beam. A severed floor beam could result in loss of controllability and rapid decompression of the airplane.