Summary
We propose to supersede an existing airworthiness directive (AD) that applies to certain The Boeing Company Model 747-100, 747- 100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747SR, and 747SP series airplanes. The existing AD currently requires repetitive inspections for skin cracks at the shear tie end fastener locations of the fuselage frames, and repairing cracks if necessary. Since we issued that AD, additional cracking has been found on an airplane not affected by the existing AD. This proposed AD would also require repetitively inspecting for skin cracks next to the shear tie on airplanes with certain existing repair doublers, and corrective actions if necessary. This proposed AD would also revise the applicability to include additional airplanes. We are proposing this AD to detect and correct fatigue cracks in the fuselage skin that can propagate and grow, and result in reduced structural integrity and sudden decompression of the airplane in flight.