Airworthiness Directives; The Boeing Company Model 747 Airplanes

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Model 747 airplanes. That AD currently requires repetitive inspections of the body station (BS) 2598 bulkhead, and corrective actions if necessary. That AD also currently requires a terminating modification for certain repetitive inspections and a post- modification inspection of the modified area. This new AD continues to require those actions using revised service information. For certain airplanes, this AD requires new repetitive inspections, an interim modification, and post-interim modification inspections. For certain airplanes, this AD requires replacing any previously repaired aft inner chord and reinstalling the terminating modification. For airplanes that are converted to the Model 747-400 large cargo freighter (LCF) configuration, this new AD reduces the threshold and repeat intervals of certain post-modification inspections. For all airplanes, this new AD also requires certain inspections of the upper aft outer chords and diagonal brace attachment fittings, flanges, and rods to continue after the terminating modification. This AD results from reports of cracked aft inner chords on airplanes after certain requirements of the existing AD were done. We are issuing this AD to prevent fatigue cracking of the BS 2598 bulkhead structure, which could result in inability of the structure to carry horizontal stabilizer flight loads, and loss of controllability of the airplane.