These are difficult times for the U.S. airline industry, what with angry passengers and politicians, outmoded air traffic control technology and a recent spike in near-collisions on runways. Meanwhile, the struggling industry continues to consolidate. Delta and Northwest are trying to merge — a move that would create the second consolidated airline since 2005 — and at least two other carriers could follow suit. The merger trend is motivated by economic realities, including major fuel price hikes. But consumer advocates and some lawmakers argue that mergers will lead to poorer service and higher costs. In recent years, hundreds of passengers have been kept on grounded planes without adequate food, water or functioning toilets for more than 10 hours in some cases. The airlines blame episodic weather events and say the government needs to modernize air traffic control. To cut costs, airlines also are outsourcing aircraft maintenance, but investigators worry whether appropriate oversight is possible for contractors abroad.