Airworthiness Directives; Boeing Model 747-400 and 747-400D Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747-400 and 747-400D series airplanes. This AD requires an inspection for corrosion and cracks of the station 980 upper deck floor beam, and repair and related investigative actions if necessary. This AD results from reports of corrosion under the cart lift threshold at the station 980 upper deck floor beam. We are issuing this AD to detect and correct such corrosion, which could result in a cracked or broken floor beam, extensive damage to adjacent structure, and possible rapid decompression of the airplane.