Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that currently requires repetitive inspections to detect cracks in various areas of the fuselage internal structure, and repair, if necessary. This amendment adds new repetitive inspections for cracking of certain areas of the upper chord of the upper deck floor beams, and repair, if necessary. This amendment is prompted by the results of fatigue testing that revealed severed upper chords of the upper deck floor beams due to fatigue cracking. The actions specified by this AD are intended to prevent loss of the structural integrity of the fuselage, which could result in rapid depressurization of the airplane.