Most U.S. airlines lost money in the first quarter, traditionally the weakest time of year for travel, but they are all eagerly looking ahead to a summer of full planes and high fares. American Airlines and Southwest Airlines said Thursday that they expect to be solidly profitable in the second quarter. They joined Delta Air Lines and United Airlines in giving an upbeat outlook for the April-through-June period, which includes the start of the peak travel season. Southwest lost $159 million in the first quarter, and American eked out a $10 million profit.
