That slowdown in passenger traffic that airlines expected after Labor Day may be coming earlier than anticipated. Most of the major U.S. carriers reported that they filled a smaller percentage of their seats in June than a year earlier, even though capacity increased modestly for most of them. The weird thing is that the only airline with double-digit growth -- AirTran Airways -- was the only one with higher load factors. As a group, the 10 largest carriers filled 84.6 percent up their seats in June, down 1.7 percentage points from June 2007. Below is a chart of the top 10 carriers for June, showing traffic, in thousands of revenue passenger miles; capacity, in thousands of available seat miles; and load factor, or percentage of seats filled with paying passengers. ...