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

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We are adopting a new airworthiness directive (AD) for all Model 747-200C and -200F series airplanes. This AD requires a high frequency eddy current (HFEC) inspection for cracks of certain fastener holes, and corrective action if necessary. This AD also requires repetitive replacements of the upper chords, straps (or angles), and radius fillers of certain upper deck floor beams, and, for any replacement that is done, detailed and open-hole HFEC inspections for cracks of the modified upper deck floor beams, and corrective actions if necessary. This AD results from a report from the manufacturer that the accomplishment of certain existing inspections, repairs, and modifications is not adequate to ensure the structural integrity of the affected 7075 series aluminum alloy upper deck floor beam upper chords on airplanes that have exceeded certain thresholds. We are issuing this AD to prevent cracking of the upper chords and straps (or angles) of the floor beams, which could lead to failure of the floor beams and consequent loss of controllability, rapid decompression, and loss of structural integrity of the airplane.