Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 747-400, -400D, and -400F series airplanes. This proposed AD was prompted by widespread corrosion damage that was found on the skin inner surface along the upper bulkhead at certain stations between certain stringers. This proposed AD would require repetitive inspections of the fuselage crown skin inner surface, and related investigative and corrective actions if necessary. This AD would also allow for terminating actions for some of the repetitive inspections. We are proposing this AD to detect and correct cracks and corrosion on the crown skin inner surface. If the cracks or corrosion are not repaired, the cracks can rapidly join together and can cause a sudden decompression and loss of structural integrity of the airplane.