The Fort-Worth-based AMR Corporation, parent company of American Airlines, has initiated a $500 million buyout of Trans World Airlines (TWA), the nation's longest flying carrier. TWA filed for Chapter 11 bankruptcy protection on Wednesday, citing high fuel prices as a major factor in its financial decline. In addition to the merger with TWA, American is also acquiring certain US Airways assets and stakes in the new Washington-based carrier, DC Air. After the merger and acquisitions, only two airlines -- American and United -- will control about half of the nation's air travel market. Another notable aspect of the TWA-American story is AMR Corporation's refusal to honor corporate raider Carl Icahn's's contract with TWA. The contract had allowed Icahn to buy heavily discounted tickets to sell on his Website, Lowestfare.com.