Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747-100B SUD, 747-200B, 747-300, 747-400, 747- 400D, and 747SP series airplanes. This proposed AD would require repetitive inspections for cracking of the crease beam and adjacent intercostals, stringers, frames, and skin panels; and related investigative and corrective actions if cracking is found. This proposed AD results from a report indicating that an operator discovered crease beam cracking on two Model 747 airplanes. We are proposing this AD to detect and correct cracking of the crease beam and adjacent structure, which could become large and result in in-flight depressurization and inability of the airframe structure to sustain flight loads.