If there is a warrant for a felony, when your passport is scanned, the terminal will say TAKE INTO CUSTODY. Then you will get to experience the wonders of Homeland Security, transfer to the local federal lockup or county jail, and then waiting to see if the state that issued the warrant wants to extradite you... assuming you are in a different state. If it is the same state, there is no extradition to worry about, go right to jail.