Dank....the President arrived on the helicopter, Marine 1 (any Marine helicopter containing the President).
He transfered to SAM 28000, which instantly becomes Air Force 1.
Air Force 1 departed the air field.
Following Air Force 1, was the backup, SAM 29000. The two planes often fly in tandem with each other....in case of any mechanical issues...and I am sure as a security precaution as well.
From what I have seen on the History Channel...I believe the planes are pretty much identical. I also believe I once heard, that they will transport additional personnel, VIP's, Media etc on SAM 29000 from time to time.