AD FAA-2013-0303

We are adopting a new airworthiness directive (AD) for certain the Boeing Company Model 747-400 and -400F series airplanes. This AD was prompted by a report of cracks on airplanes prior to line number 1308 in the forward and aft inner chords of the station (STA) 2598 bulkhead, and the bulkhead upper and lower webs. This AD requires, as applicable, repetitive high frequency eddy current (HFEC) and low frequency eddy current (LFEC) inspections for cracks in the splice fitting, support frame, forward and aft inner chords, floor support, bulkhead upper web on the upper left and right side of the bulkhead, and the bulkhead lower web on the lower left side of the bulkhead and repair if necessary; and repetitive post-repair inspections and repair if necessary. We are issuing this AD to detect and correct cracks in the splice fitting, support frame, floor support, forward and aft inner chords, and the bulkhead upper and lower webs of the STA 2598 bulkhead, which could adversely affect the structural integrity of the airplane.