Airworthiness Directives; Boeing Model 747 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires a one-time inspection to detect corrosion and cracking of the upper deck floor beam at station 980, and repair, if necessary. This amendment is prompted by reports of extensive corrosion found at station 980. Analysis of the corrosion indicated that fatigue cracking of the floor beam at this area could occur and cause the beam to break. The actions specified by this AD are intended to detect and correct such corrosion and/or cracking, which could cause the floor beam to break and result in extensive damage to adjacent structure and possible rapid decompression of the airplane.