Frontier EarlyReturns members can earn double miles on all flights to and from Washington Dulles from Aug. 19, 2014 through Oct. 10, 2014. EarlyReturns members must register for the promotion using code DBIAD prior to traveling. Double miles are also being offered for flights between Cleveland and Dallas/Fort Worth from Aug. 15, 2014 through Sept. 15, 2014 using code DBDFW and between Cleveland and Las Vegas from Sept. 4, 2014 through Oct. 4, 2014 using code LASDB. Flights between Chicago Midway and Harrisburg earn double miles through July 13, 2014 with code MDTDB and between Chicago Midway and Knoxville through July 15, 2015 using code TYSDB. For more information and a complete list of routes, visit http://insideflyerus.wpengine.com/link/?11478