Airworthiness Directives; Boeing Model 747-200B, 747-300, and 747-400 Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747-200B, 747-300, and 747-400 series airplanes. This AD requires doing repetitive detailed inspections for cracking of the aft tension tie channels from body station (BS) 1120 to BS 1220 and from BS 880 to BS 1100, and corrective actions if necessary. This AD results from cracks found in the aft tension tie channels at four station locations, on a Model 747-200B series airplane that had been modified to a special freighter. We are issuing this AD to detect and correct cracking of the aft tension tie channels; failure of more than one tension tie could result in rapid depressurization of the airplane.