The U.S. Justice Department took most everyone by surprise yesterday. Along with six states and the District of Columbia, it sued to block the merger of American Airlines and US Airways. The two airlines were just days away from a bankruptcy court hearing which they hoped would confirm their exit plan. The carriers claim their consolidation would benefit consumers by creating a new airline that could compete with rivals that have already merged. But critics and Justice officials say the transaction would result in higher fares, higher fees and fewer choices. Diane and her guests discuss the economic impact of airline mergers.