I'll think you will find that 'Air Force One' is any aircraft that the President of the United States of America is travelling on rather than a specific airframe.
i.e If he used their Aztec it would become 'Air Force One' for the day.
I hope so, otherwise I have been setting my favourite pub quizz question wrong for the last few years !!
I am also pretty certain that the fleet took at least one 400 a few years back.
[ 20 July 2001: Message edited by: TimS ]