Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes. This proposal would require a one-time inspection to detect corrosion and cracking of the upper deck floor beam at station 980, and repair, if necessary. This proposal 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 the proposed 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.