Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Model 747-100, 747-200B, and - 200F series airplanes. The existing AD currently requires inspections to detect cracking in the upper row of fasteners holes of the skin lap joints in the fuselage lower lobe, and repair, if necessary. This proposed AD would reduce the maximum interval of the post-modification inspections. This proposed AD results from reports of fatigue cracking on modified airplanes. We are proposing this AD to detect and correct fatigue cracking in the longitudinal lap joints of the fuselage lower lobe, which could lead to the rapid decompression of the airplane and the inability of the structure to carry fail-safe loads.