Summary
We propose to adopt a new airworthiness directive (AD) for all Boeing Model 747 airplanes. This proposed AD would require one-time detailed and high frequency eddy current inspections for cracks in the wing and horizontal stabilizer side-of-body joints and the fuselage skin circumferential splices, and repair if necessary. This proposed AD would also require, for certain airplanes, repetitive detailed inspections for cracks of the fuselage skin circumferential splices, and repair if necessary. This proposed AD results from Boeing analysis indicating that the wing and horizontal stabilizer side-of-body joints, and the fuselage skin circumferential splices are susceptible to fatigue cracking due to high cyclic loads on the airplane. We are proposing this AD to detect and correct fatigue cracking at multiple adjacent locations in the subject areas, which could connect to form large cracks and result in reduced structural integrity leading to rapid decompression and consequent loss of control of the airplane.