Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747-400 and 747-400D series airplanes. This proposed AD would require an inspection for corrosion and cracks of the station 980 upper deck floor beam, and repair and related investigative actions if necessary. This proposed AD is prompted by reports of corrosion under the cart lift threshold at the station 980 upper deck floor beam. We are proposing 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.