Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 747 airplanes. This proposed AD would require repetitive inspections for cracking of the fuselage frames in section 41, and corrective actions if necessary. This proposed AD results from reports of cracking in fuselage frames made of 2024 aluminum alloy that were installed during previous modification of the frames in section 41 and during production. We are proposing this AD to detect and correct frame cracks, which could result in cracking of the adjacent fuselage skin and consequent rapid decompression of the airplane.