Arriving on time was just a little bit easier for airline passengers traveling in August, in part because of a half-dozen carriers that serve Salt Lake City's airport.

The Transportation Department said Tuesday that 79.7 percent of flights arrived on time in August. That was an improvement from 78.4 percent in August 2008, and 77.6 percent in July.

Southwest Airlines Co. was the most punctual of the large carriers, with an on-time arrival rate of 82.8 percent. Continental, US Airways, and United also came in above the average of 79.7 percent. All fly in and out of Salt Lake City International Airport.

Delta, the dominant carrier in Salt Lake, was in the bottom third, at 78.6 percent. Northwest, now a subsidiary of Delta, had one of the lowest on-time rates of the big carriers, at 74.4 percent. JetBlue was only slightly better. Its on-time rate was 76 percent.

SkyWest Airlines was No. 3, with an on-time rate of 84.4 percent. Subsidiaries of the St. George-based regional operator fly for Delta and United.

Frontier Airlines, which flies between Salt Lake City and Denver, came in behind SkyWest, with an 83.8 percent on-time rate.

Airlines say the biggest cause of delays were when one late plane caused the next flight on the same aircraft to be late. Another cause was issues with the national aviation system such as airport operations, heavy traffic, and air traffic control.

Nineteen airlines report monthly on-time data and causes of delays to the Department of Transportation. The delays are labeled under categories such as "Extreme Weather" and "National Aviation System Delay" that were created by the airlines, industry groups, travel agents and government officials.

The government considers a flight on-time if it arrives within 15 minutes of schedule. Canceled and diverted flights count as late.

Hawaiian Airlines topped the list of all 19 carriers, with 94.7 percent of flights arriving on-time. Delta regional operator Comair was last, at 65.9 percent. Comair also had the highest rate of canceled flights, 4.3 percent. Continental canceled just 0.2 percent of its flights, the best of all 19 carriers.

Those on-time passengers were a little more likely to have their luggage waiting for them, too. Reports of mishandled bags fell to 4.04 per 1,000 passengers in August, down from 4.98 a year earlier. Fewer people are flying this year, and the passengers who remain are checking fewer bags because of baggage fees.

AirTran had the best baggage performance in August, with 1.74 mishandled bags per 1,000 passengers. Comair held last place by this measure, too, with 8.2 mishandled bags for every 1,000 passengers. Delta had the lowest ranking of the large carriers, with 5.02 mishandled bags for every 1,000 passengers.

Of the carriers serving Salt Lake City, Frontier had the lowest mishandled baggage rate, with 2.24 reports per 1,000 passengers.

Continental was next, at 2.89 reports. It was followed by US Airways (2.9), JetBlue Airways (2.93), Northwest (3.13), Southwest (3.57), United (4.12), and American Airlines (4.45).

Although SkyWest flights typically arrive on schedule, its mishandled baggage performance was 5.25 per 1,000 bags, below the average of 4.04.