Airworthiness Directives; Boeing Model 747 Airplanes

The FAA is superseding three existing airworthiness directives (ADs) that apply to certain Boeing Model 747 airplanes. The existing ADs currently require repetitive inspections of the body station (BS) 2598 bulkhead, and corrective action if necessary. This new AD adds a requirement to modify the bulkhead, including a one-time inspection and corrective action if necessary, which terminates certain repetitive inspections. This AD also requires a post-modification inspection of the modified area. This AD results from new reports of cracking in all three areas that require inspection in accordance with the existing ADs. We are issuing this AD to prevent fatigue cracking of the BS 2598 bulkhead structure, which could result in inability of the structure to carry horizontal stabilizer flight loads, and loss of controllability of the airplane.