Airworthiness Directives; Boeing Model 747-200F and -200C Series Airplanes

This amendment supersedes 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 amendment requires new one-time inspections for cracking of the web, upper chord, and strap of the upper deck floor beams. This action also requires modifying or repairing the upper deck floor beams, as applicable, which eventually necessitates accomplishment of new repetitive inspections for cracking of the upper deck floor beams. The actions specified by this AD are intended 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 condition.