U.S. airlines treated passengers better and improved their performance last year, minimizing the all-too familiar hassles of flying, according to a new report.

The 2011 Airline Quality Rating (AQR), an annual ranking conducted jointly by researchers at Purdue University and Wichita State University, shows that the industry's overall quality rating went up to -1.08 from -1.20 in 2010. The ranking system is based on four factors: On-time performance, mishandled bags, denied boardings, and customer complaints.

The report looks at the nation's 15 largest airlines using data from the Department of Transportation. The overall 2011 score was the best in the 22 years researchers have tracked the performance of airlines and the fourth consecutive year that performance has improved.

Among the 15 carriers rated, 10 had better overall scores than the previous year.

For the second year in a row, low-cost carrier AirTran came out on top in terms of customer service and reliability. AirTran has finished in the top two all but one year since 2004. Southwest, which recently purchased AirTran, was in the middle of the pack at No. 7 - a surprise for the perennial leader in airline customer service ratings.

Hawaiian and JetBlue rounded out the top three while regional carrier American Eagle came out on the bottom, though United drew more complaints. Delta at No. 6 was the top of the so-called legacy carriers.

According to Dean Headley, associate professor of marketing at Wichita State University, the better overall scores reflect the airline industry's efforts to be better in a capacity-limited air travel system.

As the system adjusts to increasing demand for air travel with a limited capacity of seats available, operations must be carefully handled for things to go as planned for travelers, Headley said Monday. During 2011, the industry lowered the involuntary denied boarding rate by nearly 30 percent, suggesting that most airlines are getting it together. Still, more than a third of the customer complaints for 2011 were for flight problems, such as unplanned schedule changes, delays and cancellations.

Brent Bowen, professor and head of the Department of Aviation Technology at Purdue University, said that the challenge is whether airline performance quality improvements can be maintained as more people choose to fly.

Further airline consolidation will continue to reduce the number of air carriers ranked in the AQR, he said Monday. Past AQR data suggest that the combining of two large air carrier operations often results in subsequent decreases in AQR rankings. We will be carefully watching to see if two highly rated carriers, such as No. 1 AirTran and No. 5 Southwest, will reverse this trend.

Below is the 2011 numerical ranking of the nation's leading 15 airlines, according to the Airline Quality Rating, with the 2010 ranking in parentheses:

1. AirTran (1)
2. Hawaiian (2)
3. JetBlue (3)
4. Frontier (9)
5. Alaska (4)
6. Delta (7)
7. Southwest (5)
8. US Airways (6)
9. SkyWest (10)
10. American (11)
11. Continental (8)
12. United (12)
13. Atlantic Southeast (15)
14. Mesa (13)
15. American Eagle (16)

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