** FILE ** In this Feb. 9, 2012, file photo, a Southwest Airlines Boeing 737 waits to take off at Chicago's Midway Airport as another lands. (AP Photo/Charles Rex Arbogast, File)

Photo by: Charles Rex Arbogast

** FILE ** In this Feb. 9, 2012, file photo, a Southwest Airlines Boeing 737 waits to take off at Chicago's Midway Airport as another lands. (AP Photo/Charles Rex Arbogast, File)