AD FAA-2011-0991

We are superseding an existing airworthiness directive (AD) for certain The Boeing Company Model 747-100, 747-100B, 747-200B, 747- 200C, 747-200F, 747-400F, 747SR, and 747SP series airplanes, without a stretched upper deck or stretched upper deck modification. That AD currently requires repetitive inspections for cracks of each affected tension tie and of the surrounding structure, and related investigative and corrective actions if necessary. This new AD requires, for certain airplanes, modifying the tension tie structure or tension tie and frame structure at certain stations; and a post-modification inspection of the modified area and post-modification repetitive inspections of the unmodified area, and repair if necessary. Doing the modification would terminate the repetitive inspection requirements in the existing AD. This AD reduces the compliance time and adds inspections for certain airplanes. This AD was prompted by reports that certain airplanes have tension ties that are susceptible to widespread fatigue damage. This AD also results from reports of cracks on the forward and aft tension tie channels at station (STA) 740 and STA 760, and a determination that initial inspection intervals need to be reduced. We are issuing this AD to prevent tension ties from becoming severed or disconnected from the frames, which could lead to rapid in-flight decompression.