CHICAGO (AP) â¿¿ United Airlines passenger revenue fell in August for the first time since early last year despite a slight increase in traffic. The airline, which is operated by United Continental Holdings Inc., said late Monday its passenger revenue per available seat mile fell by an estimated 0.5 percent to 1.5 percent from a year ago. That figure measures how much money the airline makes to fly a paying passenger a single mile. United said last week its share of lucrative corporate fliers has been less than it expected because of problems resulting from the blending of operational systems from United and Continental following their merger. Traffic across its main and regional network rose 0.4 percent, but that was all due to increased traffic on regional jets. Traffic on the main network alone fell 0.1 percent. A 1.2 percent decrease in domestic traffic was offset by an increase of the same amount on international flying. The number of available seats fell 0.8 percent on United's main network and 0.6 percent overall. It plans to cut flying even more than expected this year to account for sluggish demand and high fuel prices. Because traffic went up and the number of available seats went down, flights were fuller. The carrier's load factor, or occupancy rate, rose 0.9 percentage points to 86.6 percent. United, the world's largest airline is based in Chicago. Delta Air Lines Inc., United's closest competitor, said Wednesday that its passenger revenue rose 4 percent last month, helped by stable demand and an uptick in higher-paying business travelers.