AD FAA-2013-0425

We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 747 airplanes. This AD was prompted by reports of cracking in particular areas of the bulkhead structure at body station (BS) 2598. This AD requires repetitive inspections, including post-repair and post-modification inspections, for cracking in the bulkhead structure at BS 2598; certain one-time inspections of certain fasteners and support frame modifications on certain airplanes; related investigative and corrective actions, if necessary; and an interim modification that would terminate certain repetitive inspections. We are issuing this AD to detect and correct fatigue cracking of the BS 2598 bulkhead structure, which could adversely affect the structural integrity of the bulkhead and the horizontal stabilizer support structure, and result in loss of controllability of the airplane.