The budget airlines have exposed the weaknesses--and stolen customers--of woolly mammoths such as UAL's (nyse: UAL - news - people ) United, AMR's (nyse: AMR - news - people ) American Airlines and Delta Air Lines (nyse: DAL - news - people ). The old guard hopes to catch up by launching their own low-cost operations, such as Delta's new Song Air, and meeting or beating fares in cities where they compete. 
Forbes
Forbes
