Mainline traffic, which includes data from both US Airways and America West, increased to 4.69 billion revenue passenger miles, up from 4.58 billion in September 2006. A revenue passenger mile is an industry unit measuring one paying passenger flown one mile.

A 21 percent jump in trans-Atlantic travel, which corresponded with a similar increase in capacity, more than offset a slight dip in domestic traffic.

Overall capacity during the month slipped 4.8 percent to 6 billion available seat miles, compared with 6.3 billion last year. An available seat mile is an industry unit that factors in the number of seats available and the number of miles flown. The airline cut capacity in both the U.S. and Latin America.

Load factor, a measure of occupancy, jumped sharply. The airline filled 78.1 percent of its seats with paying passengers in September, compared with 72.7 percent during the same month a year ago.

Several other airlines have also reported increased September traffic figures this week.

The carrier said unit revenue increased 5 percent year over year in September, and that the trend appears to be continuing.

"The fourth quarter is showing continued signs of strong bookings on a robust fare base and we have not seen any indication of diminished demand," President Scott Kirby said in a statement.

In a regulatory filing Friday, US Airways said third and fourth-quarter unit costs would likely be higher than previously forecast because cost savings did not keep pace with reductions in capacity. The carrier now expects cost per available seat mile to rise 5 percent to 6 percent year-over-year in the third quarter, and 5 percent to 7 percent in the fourth quarter.