Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-200C and -200F series airplanes. This proposal would require repetitive inspections to find fatigue cracking in the upper chord of the upper deck floor beams, and repair if necessary. For certain airplanes, this proposal would also provide for an optional repair/modification, which would extend certain repetitive inspection intervals. This action is necessary to find and fix cracking in certain upper deck floor beams. Such cracking could extend and sever floor beams adjacent to the body frame and could result in rapid decompression and consequent loss of controllability of the airplane. This action is intended to address the identified unsafe condition.