Both Delta Air Lines and US Airways opened maintenance bases at the airport. Both bases closed during the air travel downturn following the attacks of September 11, 2001. Alabama-based Pemco World Air Services now occupies the former US Airways hangar performing MRO (maintenance, repair, overhaul) services for the Spirit Airlines and JetBlue A320 fleet. On April 1, 2010 a press release announced that a lease agreement was reached to allow Pemco to lease the second hangar formerly used by Delta Air Lines, where they perform Boeing 737 cargo conversions and modifications. Tampa Bay is one of the largest metropolitan areas in the United States that does not have a major airline hub.