[mnehring]

I believe this is a security practice going back to around the Nixon era. (there are 2 747s that could have the designation AF1 if the President is on it and in wartime, 3 E-4s that also serve this purpose so technically, there could be 5 potential AF1s.)

[Freeper]

There is never more than ONE Air Force ONE at a time. Because to be called Air Force One or Marine One or Navy One the President HAS to board.

Actually, since Obama is not really a President, I've now confused myself.