actualy, any fixed wing aircraft w/potus on it is called air force one. it came out of an atc screw up under eisenhower when an eastern airlines plane and the plane carrying ike (which used it's civialian designation of Nxxxxx) both akcnowledged the instructions due to similar call siign numbers and subsequently had to take some sort of evasive action. not sure who was at fault but ever since then, to as simply as possible identify an aircraft w/potus on it, the call sign air force one is used (and later added to include marine one for any heliocpter w/potus on it)