AirTran opperates 2 class aircraft and so does Spirit, and both make money. The point is controlled growth and also opperating frequent flights and not betting on one hub, all while keeping costs (and fares) low. All those failed carriers depended on one location, did not have enough start capital, and did not opperate frequent flights. Even B6 has 2 major bases of opperation, and they fly a lot of flights between places. Frontier has grown in a controlled manner and had about 50 million after all was said and done with startup, a nice sum, so they are able to base in DEN.