Delta Air Lines posted a big year-over-year improvement in its July on-time performance, but Delta Connection carrier Atlantic Southeast Airlines ran into problems with some chronically delayed flights over the summer.

Atlanta-based Delta posted an on-time performance rate of 79.9 percent in July -- up 10 percentage points from the same month of 2010, according to the U.S. Bureau of Transportation Statistics. That put Delta in the No. 6 spot among the largest U.S. airlines, up from No. 16 a year ago.Hawaiian Airlines, which has fewer problems with storms than other airlines, continued to hold the No. 1 spot.

Delta has put a significant focus on improving its on-time performance after a delay-ridden summer last year, including an initiative for better coordination among pilots, flight attendants and ground crew to get aircraft and passengers ready to go on time.

"This summer was much better," said Greg Kennedy, Delta's vice president overseeing the airline's Atlanta hub. "We're not perfect, but we're making great strides."Delta is working on adding more technology to eliminate lines, including the ability to print bag tags for gate-checked bags at the end of the jetway, Kennedy said.

Meanwhile, Atlanta-based Atlantic Southeast Airlines, which operates regional flights for Delta, was the only carrier in the report with chronically delayed flights for three consecutive months through July, according to the federal report. Three flights on Atlantic Southeast's route from Atlanta to White Plains had delays longer than 30 minutes more than half the time.

And airlines' cancellation rates in August will be marred by the impact of Hurricane Irene, which caused Delta to cancel more than 2,200 flights and will reduce its net profit for the month by $15 million.

"We had so many adversities this summer. We had hurricanes, we had thunderstorms, and we pulled together," said Cynthia Kay-Morris, Delta's communications coordinator for the Atlanta hub.

Separately, Delta reported two pet incidents in July, including a Labrador Retriever and a Miniature Pinscher that died.