Aviation Delta adding Seattle-Chicago service in June By Robert Silk / March 20, 2017 Share 1 -- Delta will begin flying from Seattle to Chicago O'Hare on June 19, the carrier announced Monday.Delta will service the thrice-daily route with an Airbus A319 aircraft. It will join competitors Alaska, United and American on the route. Each of those carriers fly Seattle-O'Hare at least 12 times per week. The move is part of Delta's effort to compete with Alaska at Sea-Tac airport. Alaska is still the dominant airline in its Seattle home, operating 51% of flights from Sea-Tac airport in 2016, according to the Bureau of Transportation Statistics. Delta was a distant second, operating 14% of Sea-Tac flights. Delta has more than tripled its flights out of Seattle since 2012.