Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747-200C and -200F series airplanes. The existing AD currently requires repetitive inspections to find fatigue cracking in the upper chord of the upper deck floor beams, and repair if necessary. For certain airplanes, the existing AD also provides an optional repair/modification, which extends certain repetitive inspection intervals. This proposed AD would reduce the compliance time for all initial inspections and reduce the repetitive interval for a certain inspection. This proposed AD is prompted by new reports of cracks in the upper deck floor beams occurring at lower flight cycles. We are proposing this AD to find and fix cracking in certain upper deck floor beams. Such cracking could extend and sever floor beams at a floor panel attachment hole location and could result in rapid decompression and loss of controllability of the airplane.