Delta Air Lines, Inc. (NYSE: DAL), operating as Delta Air Lines, is a major United States airline headquartered in Atlanta, Georgia, in the United States. The airline operates an extensive domestic and international network serving all continents except Antarctica. Delta Air Lines and its subsidiaries operate over 5,000 flights every day and have approximately 80,000 employees. The airline's hub at Hartsfield-Jackson Atlanta International Airport is the world's busiest airport by passenger traffic (over 91 million passengers per year) and number of landings and takeoffs. Delta is the sixth-oldest operating airline by foundation date, and the oldest airline still operating in the United States. Delta Air Lines is one of the four founding members of the SkyTeam airline alliance, the other three being Korean Air, Air France, and Aeroméxico. The loyalty program for Delta Air Lines is SkyMiles. Delta Air Lines is, as of 2012, the world's largest airline in terms of fleet size, revenue passenger-kilometers flown, and scheduled passenger traffic. Regional service for the airline is served by Delta Connection.