UUS Airways Group Inc. said on Wednesday that its flying capacity for the year will rise 2 percent, and an investor update suggested that its third-quarter profit will be bigger than Wall Street had been expecting.

US Airways has added flying capacity as it replaces old Boeing 737s with slightly larger Airbus A321s. It also completed 99.6 percent of its scheduled flights in September, which also boosts flying capacity.

For the third quarter, which ended on Sunday, the airline’s costs came in lower than expected, including a slightly lower price for fuel.

JPMorgan analyst Jamie Baker wrote that the results suggest US Airways will report a bigger-than-expected profit for the quarter. He wrote that the guidance suggests a profit of 90 cents per share, versus a consensus by a survey of analysts for 74 cents per share.

Baker wrote that some of the costs are simply shifting into the fourth quarter. That’s likely to produce a loss or maybe a break-even quarter, he wrote.

For the quarter, US Airways traffic rose 2.7 percent. Flying capacity rose 3 percent. Because the airline added more seats than passengers, its planes weren’t quite as full. Occupancy fell 0.2 percentage points to 85.8 percent.

Per-seat passenger revenue for September was flat compared to September 2011, the airline said.

For September, traffic rose 2 percent. Capacity rose 1.1 percent. That pushed occupancy up 0.7 percentage points, to 84 percent.

Shares of US Airways Group Inc., based in Tempe, jumped 99 cents, or 9.1 percent, to $11.87 in midday trading. They’ve traded between $3.96 and $14.51 over the past year, boosted by the airline’s improving financial prospects and its ongoing efforts to merge with American Airlines.