Airworthiness Directives; Boeing Model 747-100, -200, -300, 747SP, and 747SR Series Airplanes

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This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747- 100, -200, -300, 747SP, and 747SR series airplanes, that currently requires repetitive inspections to detect cracks in various areas of the fuselage internal structure, and repair, if necessary. This action would add new repetitive inspections for cracking of certain areas of the upper chord of the upper deck floor beams, and repair, if necessary. This proposal 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 the proposed AD are intended to prevent loss of the structural integrity of the fuselage, which could result in rapid depressurization of the airplane.