By John Crawley WASHINGTON, April 8 (Reuters) - Consumer complaints against big U.S. airlines fell for the first time in three years in 2001, declining 29 percent overall as more flights were on time and carriers lost fewer bags, according to a study released on Monday. But the survey by Wichita State University and the University of Nebraska at Omaha researchers noted a strong improvement in overall customer service since the Sept. 11 attacks on the U.S. as big airlines made wholesale schedule cuts and passenger volume, already hit by recession, plunged. Some of the root problems associated with past consumer complaints, like delays caused by air traffic congestion, were lower last year and disappeared altogether after Sept. 11 because there were far fewer operations by major airlines and many planes flew only half full. The study found that 10 of the 11 major airlines performed better throughout 2001 than they did in 2000, when poor customer service made headlines and got the airlines in hot water with Congress. Alaska Airlines (ALK) was the top-rated carrier last year, according to the study based on Transportation Department data. Alaska's lead ranking for baggage handling efficiency and its low record of complaints overcame a 69 percent on-time record, the worst of the major carriers. US Airways, a unit of US Airways Group (U), was second in customer satisfaction even through it is struggling financially. Northwest Airlines (NWAC) was third, followed by Southwest Airlines (LUV), last year's No. 1, Delta Airlines (DAL), American Airlines (AMR), America West (AWA), Continental Airlines (CAL), United Airlines (UAL), American Eagle, a unit of American, and TWA, which was bought by American. All of the airlines showed customer service improvement except Delta, which basically performed the same as it did the previous year, when it topped all the others. In a companion survey of 500 frequent fliers conducted last month, the researchers found that the top customer service concern was lost baggage. On-time service was fifth. With many major carriers reducing capacity by up to 20 percent in the final 3-1/2 months of last year, the skies were less crowded and operations were smoother than during the corresponding period in 2000 -- a year of record delays and congestion as well as soaring consumer dissatisfaction. "The post 9/11 on-time performance of a down-sized air transport system was 7 percent better than earlier months in 2001," said Dean Headley, a marketing professor at Wichita State and a co-author of the 12th annual airline quality report. "Baggage handling and customer complaints also showed improvement in the last quarter. Let's hope the carriers learn from this and continue to improve customer service as we return to a full capacity system," he said. While air travel has slowly rebounded since October, the government and industry do not expect traffic to return to its pre-Sept. 11 level until later this year or early next, barring another terror attack or a worsening economic picture. Passenger traffic on U.S. airlines for domestic and international travel was off almost 12 percent in 2001 to 682 million, largely due to the double whammy of recession and the fallout from the Sept. 11 attacks. On average, the Transportation Department received 2.11 consumer complaints per 100,000 passengers for the 11 largest carriers in 2001, the study showed, a 29 percent drop over 2000. -- On-time arrival percentage improved almost 5 percent to 77.4 percent last year from 72.6 percent in 2000. Southwest had the best on-time record at 81 percent. -- Denied boardings per passenger decreased from 1.04 per 10,000 passengers in 2000 to 0.86 percent last year. TWA had the worst bumping rate while US Airways was least likely to bump a passenger. -- Mishandled baggage rates improved from 5.29 per 1,000 passengers in 2000 to 4.55 per 1,000 passengers in 2001. American Eagle was the worst for mishandled baggage, while Alaska had the highest rating for baggage efficieny. In a footnote to the study, the researchers said complaints mailed to the Transportation Department after postal delivery in Washington was interrupted by the anthrax scare were not received or arrived too late for inclusion in the annual data. About half of airline consumer complaints to the government are mailed, while the rest are e-mailed. ©2002 Reuters Limited.