Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for certain Boeing Model 747-100, -100B, -100B SUD, -200B, and -300 series airplanes; and Model 747SR and 747SP series airplanes. That AD currently requires repetitive inspections to detect fatigue cracking in the upper deck floor beams located at certain body stations, and repair, if necessary. This proposed AD would lower the threshold for the existing inspections and would require new repetitive inspections of previously repaired areas, and repair if necessary. This proposed AD is prompted by the results of an additional detailed analysis that indicate fatigue cracks can initiate sooner than has previously been observed. We are proposing this AD to prevent failure of the upper deck floor beams at certain body stations due to fatigue cracking, which could result in rapid decompression and reduced controllability of the airplane.