AirTran Airways' chief believes legacy carriers will continue to shed seats in the U.S. market because they have had a hard time making money domestically.

CEO Bob Fornaro told investors at a New York conference on Thursday that AirTran can make money in the U.S. because it has low costs, allowing it to offer cheap fares while still posting profits.

AirTran plans to increase capacity, which is measured by the available seats an airline offers times miles flown, by 3 percent to 4 percent this year.

The five U.S. legacy carriers are Delta Air Lines, American Airlines, United Airlines, Continental Airlines and US Airways. Legacy airlines are those that had a large presence in multiple regions of the country before deregulation of the industry in 1978.