The nation's airlines posted worse on-time rates in May, and Chicago airports ranked last for on-time departures.
Airlines were on time 76.9 percent of the time, according to data released on Wednesday by the U.S. Department of Transportation. That's down from 79.4 percent in May 2013 and 79.6 percent in April.
Just 0.6 percent of flights were delayed because of weather. Late-arriving aircraft, carrier delays and aviation system delays were the biggest factors, according to the Air Travel Consumer Report.
Southwest Airlines was the worst among large carriers; its on-time rate was 72.7 percent.
Most punctual airlines were Hawaiian, 93.2 percent; Alaska, 89.7 percent; and Delta, 84.4 percent.
