Airworthiness Directives; Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP Series Airplanes

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The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP series airplanes. The existing AD currently requires an inspection to determine if acceptable external skin doublers are installed at the stringer 6 (S-6) lap splices, between station (STA) 340 and STA 400. For airplanes without the acceptable external skin doublers, the existing AD requires repetitive related investigative actions and corrective actions if necessary. The existing AD also provides an optional terminating modification for the repetitive related investigative actions. This proposed AD would mandate the optional terminating modification. This proposed AD results from a report of cracked fastener holes at the right S-6 lap splice between STA 340 and STA 380. We are proposing this AD to prevent cracking in the fuselage skin, which could result in rapid decompression and loss of structural integrity of the airplane.