The world's airlines are scheduling some 4.9% more seats this September than the same month in 2010, translating into a 6.7% increase in ASKs. These are similar to the capacity increases witnessed in the peak summer month of August, suggesting the leading airlines are confident about growth prospects. Delta Air Lines remains the world's biggest carrier this month, despite trimming its ASKs by 2.1% year-on-year. United (-4.3%) and US Airways (-2.2%) are the only other carriers in the Top 25 that are reducing their capacity year-on-year. United-Continental however is the world's biggest combination, maintaining a margin of some 5.5% above Delta in terms of ASKs.