The Transportation Department says it received 1,062 complaints about airline service in May. That's up 20.8% from the 879 complaints filed in April and 33% higher than the 799 received in May 2010, according to the department's Bureau of Transportation Statistics.

The department monitors the domestic performance of the 16 largest U.S. airlines.

More than 380 complaints were filed about problems related to delays, cancellations and missed connections. That's up from 226 the year before. Complaints about customer service rose to 120 compared with 87 a year ago.

Other categories of major complaints about service — refunds, fares and handling disabled travelers — also showed sharp increases.

Large airlines not surprisingly were the target of more complaints. American Airlines had the most with 147, followed by Delta Air Lines with 107 and United Airlines with 101. Continental Airlines, which merged with United but reports separately to the government, received 72 complaints.

"The actual number of complaints is 1.29 per 100,000 enplanements, a very small number," says Steve Lott, a spokesman for the Air Transport Association. "There was a total of 55 million enplanements in May."

Other airline performance indicators monitored by the Transportation Department — the rate at which flights arrived on time and long delays on airport tarmacs — also worsened in May.

Bad weather triggered systemwide delays at key hub airports, and the nation's 16 largest airlines posted an on-time arrival rate of 77.1% in May. That's down from 79.9% a year ago but slightly better than April's 75.5%, the bureau's statistics show. A flight is considered on time if it arrives within 15 minutes of its schedule.

Indicative of the role severe thunderstorms in large parts of the country played in May: About 42% of all late flights were affected by weather compared with 39% a year ago and 40% in April.

After several months of no or minimal incidents involving lengthy tarmac delays of more than three hours, the airlines reported 16 of them in May. All but two were reported by American Eagle Airlines flights arriving at Chicago's O'Hare on May 29, when thunderstorms and heavy winds canceled a large volume of flights.

A year ago, only one flight reported a tarmac delay of more than three hours. That was the first full month that the government imposed a rule that triggers an investigation that could lead to a fine of $27,500 per passenger if a plane is held on a tarmac for more than three hours without taking off or letting passengers off.

The airlines canceled more flights in May: 10,754 flights — or 2.1% of 520,612 operations — were called off. That compares with 1.2% a year ago and 2% in April.

"Many U.S. airlines were challenged by extreme weather during May that made conditions unsafe to fly and led to a higher rate of canceled flights," Lott says.

Other performance findings from May:

•More mishandled bags. The airlines reported a rate of mishandled bags of 3.52 per 1,000 passengers. That's up from both May 2010's rate of 3.23 and April's 3.24.

•Hawaiian Airlines , which mostly flies among the islands, had the highest on-time arrival rate, followed by Alaska Airlines and AirTran. American Eagle Airlines and American Airlines — both owned by Fort Worth-based AMR — reported the worst on-time rates, respectively.

•American Eagle and American Airlines reported the highest flight cancellation rates: 6.6% and 5.5% respectively.