Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 747- 100 series airplanes, that currently requires repetitive inspections to detect cracking of the outer chord of the body station (BS) 1480 upper and lower bulkhead and longeron splice fitting; repair, if necessary; and modification of the skin splice plate, the outer chord splice fitting, and the stringer interface of the lower bulkhead, if necessary. This action would revise the applicability of the existing AD to add additional airplanes, require accomplishment of previously optional inspections and clarify those inspections, extend certain compliance times, and require additional work in certain areas. This proposal is prompted by reports that fatigue cracking has been found in the outer chord of the BS 1480 bulkhead at the overwing longeron splice on airplanes not subject to the existing AD. The actions specified in this proposed AD are intended to detect and correct fatigue cracking of the outer chord of the BS 1480 upper and lower bulkhead and longeron splice fitting, which could result in reduced structural integrity of the fuselage and the inability to carry limit load.