Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for certain Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-300, 747SP, and 747SR series airplanes. That AD currently requires one-time inspections for cracking in certain upper deck floor beams and follow-on actions. This proposed AD would expand the existing inspection area, and would require inspecting fastener holes in certain areas of airplanes modified previously, and taking corrective actions if necessary. This action also would define new sources for instructions for repairs and post-modification/repair inspections. This proposed AD is prompted by reports of fatigue cracking of the upper chord of certain upper deck floor beams. We are proposing this AD to find and fix cracking in certain upper deck floor beams, which could extend and sever floor beams adjacent to the body frame and result in rapid depressurization and loss of controllability of the airplane.