American Airlines is adding year-round flights from Philadelphia International Airport to Asheville, N.C., and Chattanooga, TN, starting May 3, 2019. Tickets go on sale Monday, the airline said Friday. Next May, American will also start operating its PHL-Prague route on a bigger plane — an Airbus A330-200. That opens up more than 500 additional seats on the route every week, and means passengers can opt for Premium Economy tickets.