Airlines improved their performance last year, with fewer lost bags and bumped passengers due to overbooking and more on-time arrivals, but travelers were still dissatisfied, according to an annual study of airline quality.

Complaints to the Department of Transportation about airline performance went up a whopping 28 percent in 2010, the study said.

A precise cause for the spike in consumer disenchantment is hard to nail down, but it’s most likely due to changes in the way airlines are doing business, said Dean Headley, co-author of the report, which is based on Transportation Department data.

The number of air travelers is increasing, but there are fewer flights and fewer seats available. So flights are more crowded, and it’s tougher to rebook when a flight is canceled.

“They are trying to match supply and demand – the number of seats available to the number of people demanding seats – a lot closer so they don’t fly empty seats, which is expensive for the airlines,” said Headley, an associate professor of marketing at Wichita State University’s W. Frank Barton School of Business.

That increases the chances that some passengers are going to be unhappy because mismatches between passengers and seats available usually are managed to the airline’s advantage, he said.

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“Even though airlines are vocal about saying they want to please the customer, when it comes right down to it, they’re going to make money first,” Headley said.

There were 1.22 complaints per 100,000 passengers last year, compared with less than 1 per 100,000 in 2009.

An overall ranking of the nation’s 16 largest airlines based on their combined performance in four categories – on-time arrivals, mishandled baggage, denied boardings, complaints – was coming out at 9:30 a.m. EDT Monday.

The department doesn’t keep records on the number of flight cancellations, but the biggest category of complaints was “flight problems,” which includes cancellations and delays.

How the 16 largest U.S. airlines stacked up, based on the number of complaints per 100,000 passengers:

-Delta Airlines, 2

-United, 1.64

-US Airways, 1.53

-Continental, 1.48

-American, 1.44

-Frontier, 1.23

-Comair, 1.25

-JetBlue, 1.25

-Hawaiian, 1.16

-American Eagle, 1.03

-AirTran, 0.90

-Skywest, 0.61

-Atlantic Southeast, 0.54

-Mesa, 0.53

-Alaska, 0.44

-Southwest, 0.27