Airlines curbed delays in July, but Aug. won't be as good

— -- U.S. airlines curbed delays at the height of the summer travel season. But their improved on-time performance in July will be erased by Tropical Storm Irene when August data are released next month.

The 16 largest carriers delivered 77.8% of their flights on time in July. That's better than 76.7% a year ago and better than June's 76.9%, according to data released Monday by the Transportation Department's Bureau of Transportation Statistics.

About 38% of late flights were delayed by bad weather, the bureau says. A flight is considered on time if it arrives within 15 minutes of schedule. Airlines that handle at least 1% of domestic traffic are required to report performance data to federal regulators.

Hawaiian Airlines, which mostly flies among the islands, took its usual top spot as the carrier with the most prompt service. Alaska and Southwest airlines followed.

Regional airlines that fly as feeder carriers for larger partners — Atlantic Southeast and ExpressJet airlines — fared the worst.

There also were fewer three-hour-long tarmac delays in July after the number reached double digits in May and June for the first time since a new Transportation Department rule took effect last year aimed at limiting them. The carriers reported only one tarmac delay of more than three hours in July, compared with 14 in June.

Last year, the department introduced a new rule that can lead to airline fines of up to $27,500 per passenger for a flight that sits on the tarmac for more than three hours.

Federal regulators have yet to fine any carriers, finding that most of the three-hour-plus delays were not in violation and fall under the exceptions provided in the rule. The exceptions: safety or security, or if air traffic control advises the pilot that returning to the terminal would disrupt airport operations.

The carriers canceled 1.7% of their scheduled domestic flights in July — or 9,232 of 547,219. That's up from 1.4% of a year ago but down from 1.8% in June.

The modest July improvements will give way to the havoc brought by Irene in late August, and next month's federal data will show a sharp deterioration. With the storm forcing major East Coast airports to shut down during the last weekend of August, hundreds of thousands of travelers were left stranded as airlines canceled more than 14,000 flights.

Other findings from the July report:

•More mishandled bags. The carriers reported a mishandled baggage rate of 3.71 reports per 1,000 passengers in July, up from 3.69 a year ago.

•More complaints. In July, the department received 1,285 complaints about airline service from consumers, up from both 1,097 filed a year ago and 1,127 received in June.

•Airport results. Salt Lake City (86.0%) reported the highest on-time performance of the 29 busiest airports in July. Newark (65.6%) and San Francisco (65.7%) had the most delays. Portland, Ore., (89.1%) scored the highest on-time departure rate, while Chicago O'Hare (68.8%) had the lowest.