Although the tag "Air Force One" can be used for any U.S. Air Force aircraft that carries the president, the ones it is referring to are the two pimped out Boeing 747s used solely by the president and any White House approved "passengers" - the White House press corps, advisors, staff, and "guests".
The two planes, which in aviation speak are referred to as VC-25 A's, are virtually an airborne version of the White House's administrative wing, offering 4,000 square feet of floor space over three levels. The current Air Force Ones have not been upgraded since 1990 apart for some new technology.
Joseph W. Hagin, deputy chief of staff under President George W. Bush says, "You can hang new engines on it, you can cram all sorts of new technology on it, but it's still a very old airplane."
The Air Force has requested two new Air Force Ones with its preference being Boeing 747-8's. The commercial model of the 747-8 is quieter, has more fuel-efficient engines, is bigger, more powerful and has vastly superior technology than the current VC-25A's. Of course, Air Force One will only be built on the frame of the Boeing 747-8. The new planes will contain all the extra security and technology gadgets needed by the president to run the free world, and demanded by his security team.
The new generation of Air Force One won't come cheap. The Air Force has requested $3 billion for the project, which even if approved today, would not be ready for delivery until 2023.
The U.S. Air Force is not the only one shopping for a customised Boeing 747-8. According to Boeing, an anonymous buyer recently purchased a VIP version of the aircraft with 4,786-square-feet of useable space, which is even bigger than the customized Airbus of Saudi Arabian Prince Walid bin Talal, which has 6,400 square feet of airborne luxury.