In the United States, airline carriers such as Midway Airlines and America West Airlines, which commenced operations after 1978, soon realized a cost of available seat mile (CASM) advantage in relation to the traditional and established, legacy airlines such as Trans World Airlines and American Airlines. Often this CASM advantage has been attributed solely to the lower labor costs of the newly hired and lower pay grade workers of new start-up carriers, such as ValuJet, Midway Airlines, and their like. However, these lower costs can also be attributed to the less complex aircraft fleets and route networks with which these new carriers began operations, in addition to their reduced labor costs.