Summary
We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 747-400, 747-400D, and 747-400F series airplanes. This proposed AD would require installing an extension tube to the existing pump discharge port of the scavenge pump on the outboard side of the center fuel tank in the main fuel tank 2. This AD results from fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent a fire or explosion in the fuel tank and consequent loss of the airplane.