Southwest Airlines (NYSE:LUV) could become Denver International Airport’s largest carrier in a year or so, according to an aviation consultant, as United Airlines juggles its fleet.The consultant, Michael Boyd, said that United Airlines has outsourced many flights to regional airline affiliates.United and Continental had about 30% of the domestic passenger market in March at Denver International Airport.Southwest Airlines has a potential upside of 37.1% based on a current price of $12.4 and an average consensus analyst price target of $17.