The Trump administration is set to accept a $400 million luxury 747-8 from the royal family of Qatar – a lavish "palace in the sky" meant as a temporary Air Force One. But getting it up to presidential security standards could take years and cost hundreds of millions more.

Technically, any US Air Force aircraft carrying the president is designated "Air Force One" by air traffic control. Biden even took a train informally dubbed "Rail Force One." For long-haul flights, presidents have relied on one of two VC-25As - heavily modified Boeing 747-200Bs - since 1990.

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What Makes Air Force One, Air Force One

The current VC-25s aren't just repainted 747s. They're a pair of flying fortresses that must be capable of allowing the president to run the country, survive wartime conditions (even nuclear), and be totally secure from outside influence or intrusion.

While the precise details of the current airframe are a tightly guarded secret, some details are included on government fact sheets or have been revealed in various media reports. For a start, it must have an in-flight refueling capability so the president can go anywhere in the world and stay up as long as needed. Retrofitting this to an existing 747 would be very expensive, as the feds would need to strengthen portions of the hull to handle the refueling system and reconfigure the fuel tanks to handle trim issues.

Then there's the hull, which is known to be armored, and the windows are also thicker than you'd find on a normal flight. The government would also need to build in weapons systems like the chaff rockets used against radar-guided missiles, flares against heat seekers, and AN/ALQ-204 Matador Infrared Countermeasure systems, or similar to try and confuse incoming missiles.

Next up, the engines and electrical systems would have to be replaced. The electronics in the current VC-25s are hardened as much as possible against an electromagnetic pulse that would be generated by a nuclear detonation. There are also claims that the aircraft have extra shielding in the engines to help against missile fragments should a physical attack happen.

Next up are communications. Air Force One has air-to-ground, air-to-air, and satellite comms systems that are thought to be the equal of what's in the White House. There are at least two separate internal phone systems - one open and the other highly secure - that would need to be installed and checked as well.

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