Presidential aircraft haven't always been Boeings.Though the first de-facto aircraft was a B314 several Douglas and Lockheed models have also been used.DC6 and DC7, and Constellations for example.You are correct when you refine your point to state that all purpose built presidential aircraft have been supplied by Boeing, but that is hardly surprising as there have only been 2 types of those (VC137 and VC25).Air Force One of course can be anything. If President Bush were to decide to get his type rating for the F-15 (as an upgrade from his F-102) the one he's be flying at any time would be Air Force One as that is simply the designated callsign for whichevery USAF aircraft has the president on board.When the president is not on board the VC25s will never use the callsign.

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