A total of 21 percent of commercial flights in the U.S. arrived at least 15 minutes late, were canceled or diverted in May, according to the Transportation Department's Bureau of Transportation Statistics.
That is down from more than 22 percent of late flights in the same month last year and in April of this year. The previous month's figure was higher in part because AMR Corp.'s American, the nation's largest carrier, was forced to ground thousands of flights amid tighter government scrutiny of maintenance issues.
The latest government figures show American again had the most delays, getting passengers to their destinations as scheduled only 67.3 percent of the time. It was followed by UAL Corp.'s United Airlines, the second-largest carrier, which reported 72.4 percent of on-time arrivals, and Continental Airlines Inc., with 75.4 percent.
Weather was by far the biggest cause of late flights in May, accounting for just over 44 percent of all delays. Only about 39 percent of flights were late because of weather a year earlier.
U.S. carriers also improved their baggage handling in May. About 4.6 passengers out of every 1,000 reported a mishandled bag during the month, compared with nearly 6 per 1,000 a year earlier and 5 per 1,000 in April.
Reported passenger complaints fell to 885, compared with 930 a year earlier and 1,113 in April.
The U.S. airline industry is straining under record-high fuel prices, which have prompted many carriers to raise fares, announce sweeping flight cutbacks and begin charging for amenities such as checked bags and extra legroom.
Oil prices fell sharply Monday but nonetheless remain within range of last week's all-time highs. Light, sweet crude for August delivery fell $4.54 to $140.75 by midday on the New York Mercantile Exchange.