The current 747s are getting rather long in the tooth. They entered service while Bush 1 was in office. Of course, they've had some upgrades but most planes from that time period are either stored in the desert or were scavenged for parts. Dubya revealed recently that on 9/11 AF1 did not have the capability to permit him to have secure conference calls. Boeing's latest version of the 747 is being touted as the replacement. (an Airbus A380 is too). I know it likely will be a long time before a president dare even suggest replacing the current planes. It would be cannon fodder for the oposition, populists and Tea Party loons. The direct and ripple effect jobs situation is something they don't think about.