The B Concourse will be closed during construction, and airlines and tenants will move to the A and C Concourses during that time. The south end of the C Concourse will remain intact until the B Concourse is completed and airlines have moved from C to B. The southwest leg of the B Concourse will be updated in a future phase, and will only be utilized in the near term for passengers from inbound international flights. On April 4, 2018 Delta Air Lines moved to the A Concourse and Allegiant Air to the C Concourse; construction on the B concourse began in September 2018. Thanks to factors such as the addition of Southwest Airlines and other low cost carriers, airport traffic has been rebounding in recent years. Memphis International Airport has one terminal and three concourses. In 2021, all flights will consolidate to Concourse B and A and C will be mothballed. Concourse A has 9 gates. Concourse B has 42 gates. Delta Air Lines operates a Sky Club lounge outside Concourse B. The concourse contains the airports U.S. Customs and Border Protection facility, which is used on a limited basis for charter flights. Concourse B is closed for work on the airport's modernization project, expected to be completed in 2021. Concourse C has 18 gates.