What president took off in Air Force One, but didn't land in Air Force One? (p.s. DG can't answer cuz I already told him the answer...)

Unfortunatly, That was my old boss, Richard Nixon

SR, can you tell me how it happened?

Yes, (if you must rub salt in the wound)! President Nixon resigned the Presidency, took off on "Air Force One" (any plane bearing the President has that call sign).
While over the mid-west, Gerald Ford was sworn in as President, therefore the plane carrying President Nixon changed its call sign to SAM (Special Air Mission 26000, N-26000 being its tail number), as he was no longer President. Colonel Ralph Albertazzie, a Nixon supporter (and a friend of mine), had the dubious and sad distinction to make the radio call changing the plane's designation; A very sad day for me and many others who worked for, and respected him.

great answer SR! It's surprising how when I ask people so many of them try to think of a president who went skydiving.