Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747- 200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes. The original NPRM would have required inspections for scribe lines in affected lap and butt splices, wing-to-body fairings locations, and external repair and cutout reinforcement areas; and related investigative and corrective actions if necessary. The original NPRM resulted from reports of scribe lines found at lap joints and butt joints, around external doublers and antennas, and at locations where external decals had been cut. This action revises the original NPRM by revising certain compliance times including reducing the compliance time for certain repetitive inspections. This supplemental NPRM also proposes to add inspections for certain airplanes. We are proposing this AD to detect and correct scribe lines, which can develop into fatigue cracks in the skin and cause sudden decompression of the airplane.