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

We are adopting a new airworthiness directive (AD) for certain Boeing Model 747-100, 747-100B, 747-200B, 747-200C, 747-200F, 747-300, 747SR, and 747SP series airplanes. This AD 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, this AD requires repetitive related investigative actions and corrective actions if necessary. This AD also provides an optional terminating modification for the repetitive related investigative actions. This AD results from a report of cracked fastener holes at the right S-6 lap splice between STA 340 and STA 380. We are issuing this AD to detect and correct cracking in the fuselage skin, which could result in rapid decompression and loss of structural integrity.