Summary
The FAA proposes to supersede 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 proposed AD would add a requirement to modify the bulkhead, including a one-time inspection and corrective action if necessary, which would terminate certain repetitive inspections. This proposed AD would also require a post-modification inspection of the modified area. This proposed AD results from new reports of cracking in all three areas that require inspection in accordance with the existing ADs. We are proposing 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 reduced controllability of the airplane.