Airworthiness Directives; Boeing Model 747-100B SUD, 747-200B, 747-300, 747-400, 747-400D, and 747SP Series Airplanes

The FAA is adopting 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 AD requires 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 AD results from a report indicating that an operator discovered crease beam cracking on two Model 747 airplanes. We are issuing 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.