Airworthiness Directives; The Boeing Company Model 747-200B Series Airplanes

We are adopting a new airworthiness directive (AD) for certain Model 747-200B series airplanes. This AD requires repetitive inspections for cracking of the fuselage skin lap joints at stringer 6 on the left and right sides from station (STA) 340 to STA 400, a one- time general visual inspection to determine if certain fasteners are installed and to determine if service repair manual (SRM) repairs or repair doublers are installed, and corrective actions if necessary. Doing an optional modification of the stringer 6 lap joints terminates the repetitive inspections for the modified area. This AD results from reviews done by Boeing, which show that airplanes that were modified by Boeing to the stretched upper deck (SUD) configuration require inspection for cracking of the stringer 6 lap joint upper-fastener row earlier than previously expected. We are issuing this AD to detect and correct cracking of the stringer 6 lap joints where certain external doublers were not installed, which could result in rapid decompression and loss of structural integrity of the airplane.