Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200F, 747-300, 747SP, and 747SR series airplanes. This proposal would require one-time inspections for cracking in certain upper deck floor beams and follow-on actions. 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 result in rapid depressurization of the airplane. This action is intended to address the identified unsafe condition.