Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to all Boeing Model 747-200F and -200C series airplanes, that currently requires repetitive detailed inspections or a one-time open-hole high frequency eddy current inspection to detect cracking of certain areas of the upper deck floor beams, and corrective actions if necessary. This action would add new one-time inspections for cracking of the web, upper chord, and strap of the upper deck floor beams. This action also would add a requirement to modify or repair the upper deck floor beams, as applicable, which would eventually necessitate accomplishment of new repetitive inspections for cracking of the upper deck floor beams. This action is necessary to prevent fatigue cracks in the upper chord and web of upper deck floor beams and the resultant failure of such floor beams. Failure of a floor beam could result in damage to critical flight control cables and wire bundles that pass through the floor beam, and consequent loss of controllability of the airplane. Failure of the floor beam also could result in the failure of the adjacent fuselage frames and skin, and consequent rapid decompression of the airplane. This action is intended to address the identified unsafe conditions.