airTran never said it directly, but it is clear from this DOT submission that they want Baltimore-Cancun:
They are asking DOT to postpone renewing United's Dulles-Cancun authority, and saying that USA 3000 basicly shouldn't have WAS-CUN authority, because they are essentially providing a scheduled charter service. They never mention they want to fly BWI-CUN, but it is obvious that's what they are looking for.
They also argue it is senseless that DCA/IAD and BWI are both considered Washington, D.C. I agree strongly with this latter point. MIA/FLL and SFO/OAK are seperate, and they are considerably closer to each other than DCA/IAD and BWI.