Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747-100, -100B, 100B SUD, -200B, and -300 series airplanes; and Model 747SP and 747SR series airplanes. This proposed AD would replace certain requirements of an existing AD. This proposed AD would require repetitive inspections to detect cracks in various areas of the upper deck floor beams, and repair if necessary. This proposed AD is prompted by the results of fatigue testing that revealed severed upper chords of the upper deck floor beams due to fatigue cracking. We are proposing this AD to detect and correct cracking in the upper chords of the upper deck floor beams. Undetected cracking could result in large deflection or deformation of the upper deck floor beams, resulting in damage to wire bundles and control cables for the flight control system, and reduced controllability of the airplane. Multiple adjacent severed floor beams could result in rapid decompression of the airplane.