Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 747 airplanes. This proposed AD would require repetitive external surface high frequency eddy current inspections to detect cracks in the radius detail of the upper lobe doubler on both sides of the airplane, and applicable corrective action. This proposed AD results from reports of cracks in the radius detail of the upper lobe doublers. We are proposing this AD to detect and correct cracks in the upper lobe doublers. Such cracks could result in significant degradation of the fuselage structure and reduce its ability to carry flight loads from the vertical stabilizer, which could adversely affect the controllability of the airplane.