Airworthiness Directives; Boeing Model 747-200B, -200C, -200F, and -400F Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747 series airplanes. This AD requires repetitive detailed inspections for cracks in the crease beam and adjacent structure of the fuselage, and related investigative and corrective actions if necessary. This AD is prompted by fatigue cracks found in the crease beam during a follow-on inspection of a previously installed modification. We are issuing this AD to find and fix fatigue cracking of the fuselage frame, which could result in reduced structural integrity of the frame and consequent rapid decompression of the airplane.