Southwest Airlines’ planned buyout of AirTran would have an impact on Missouri’s two busiest airports. But officials don’t yet know what it will be. Southwest is the largest passenger carrier at St. Louis and Kansas City’s airports. Southwest now has 62 nonstop flights a day from Kansas City. AirTran has three. AirTran has eight flights from St. Louis, where Southwest controls more than 40% of the business, almost double the amount done at Lambert by American Airlines.