Passenger traffic and a key revenue figure rose in December at American Airlines and US Airways, echoing similar results at other big U.S. carriers.
The airlines benefited from strong holiday travel demand, and December results were bolstered by the unusually late Thanksgiving Day, which pushed some return trips from November into early December.
The two carriers merged to create American Airlines Group Inc., but they reported separate statistics for December on Thursday.
The company's shares rose $1.49, or 5.4 percent, to $29.12 in midday trading. They began the day up 15.4 percent from their opening price on Dec. 9, when the merger closed and created the world's biggest airline operator.
The Fort Worth-based company said that passenger revenue for every seat flown one mile last month rose about 9 percent on American Airlines and 12 percent on US Airways, compared with December 2012. The estimates include regional flights such as American Eagle.
The per-mile figure is a closely watched measure of revenue performance in the airline business, and it increases when average ticket prices rise and when more seats are filled.
Traffic on American and its regional affiliate rose 5 percent, as passengers flew 11.86 billion miles. American increased passenger-carrying capacity by 1.1 percent, with a decline in domestic seats but a 14.1 percent jump in capacity across the Atlantic and 5.1 percent to Latin America.
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The average flight on American and Eagle was 83.3 percent full, compared with 80.2 percent in December 2012.
At US Airways and its regional airlines, traffic jumped 7 percent to 6.29 billion miles. Capacity rose 3.6 percent and the average plane was 84.7 percent full, up from 82 percent a year earlier. Unlike American, US Airways increased capacity in the U.S. by 5 percent.
Thursday's report came after similar strong December revenue-per mile figures posted in the past week by United Airlines, Delta Air Lines and Southwest Airlines.