Airworthiness Directives; The Boeing Company Airplanes

We are superseding airworthiness directive (AD) 90-23-14 for certain The Boeing Company Model 747 series airplanes. AD 90-23-14 required inspections of the fuselage skin lap splice between body station (BS) 340 and BS 400 at stringers (S)-6L and S-6R, and repair if necessary. This new AD adds new repetitive inspections for cracking in the S-6 skin lap splice, which terminates the inspections required by AD 90-23-14; eventual modification of the lap splice, which terminates the repetitive inspections; post-modification inspections; and corrective actions if necessary. This AD also adds airplanes to the applicability. This AD was prompted by a report of cracks up to 18.5 inches that were found at S-6L and S-6R on several airplanes, and subsequent analysis results that indicated that the protruding head fastener modification and related post-modification inspections required by AD 90-23-14 are not adequate to prevent cracking at the upper row of fasteners in the S-6 lap joint before the cracks reach a critical length. We are issuing this AD to detect and correct cracking at the upper row of fasteners in the S-6 lap joint, which could result in a sudden loss of cabin pressurization and the inability of the fuselage to withstand failsafe loads.