Utilizing Concourse A mostly, United Airlines operates out of Terminal at St. Louis Lambert International Airport (STL). United Airlines At STL Terminal there are several ways to check in at the terminal, including self-service kiosks and counters. Following check-in, travelers go through a centralized security checkpoint; TSA PreCheck is offered for those who qualify. Despite not having a lounge of its own, United has a number of food and retail options at STL. Passengers have several options for ground transportation, including taxis, ride-sharing services, rental cars, and the MetroLink light rail, which links the airport to various locations, including downtown St. Louis.