In the early 1990s, United Airlines began flights between Manchester and Washington Dulles International Airport near Washington, D.C. But creation of a north–south hub at Dulles did not work for United, and heavy competition in this market led to a quick exit. The Boeing 737 was used for this short-lived service, which comprised about four daily circuits between the two airports. US Airways started service at Manchester in early 1986, by connecting their hubs at Pittsburgh and Philadelphia. The carrier used the DC-9, BAC 111, and 737-200 aircraft. Both carriers expanded service at Manchester over the years with larger planes and more flights. United now runs a strict non-stop schedule to and from Chicago with no intermediate stops or tag-ons. The 757 has been used by both United and US Airways at Manchester, which stands as the largest passenger-carrying plane to serve the airport in scheduled service. The Airbus A320 series of aircraft is also commonly used by United, Northwest Airlines (merged with Delta Air Lines), and occasionally by US Airways. In April 2010, Delta enhanced service to Manchester; it dropped its daily CRJ-700 service to Atlanta and replaced the aircraft with an MD-88 with seating for 149. Delta also switched all its Delta Connection service to Detroit with mainline service on DC-9's. Southwest is the only airline currently serving Manchester with mainline aircraft such as the Boeing 737-700 and the Boeing 737-800, along with American, who seasonally flies the Airbus A319/320 from Philadelphia.