American and other U.S. airlines are soaring as mergers have helped them limit the number of flights, keeping fares higher, and falling oil prices have given them relief from their largest expense, jet fuel. The net income reported by American Airlines Group Inc. was an 87 percent increase over the $505 million earned by American and US Airways a year earlier, when they were still separate companies. The amount that passengers paid to fly each mile, called yield in the airline business, was a record, reflecting strong demand and average fares.