JetBlue was once again ranked as offering the best service in an annual survey that also found five of the top six airlines are low-fare carriers.

AirTran Airways, Southwest Airlines, and United rounded out the top of the national Airline Quality Rating study, released Monday.

“JetBlue probably has the right mix of services and management to maintain and secure this top position,” said a co-author of the report and director of the University of Nebraska’s aviation institute, Brent Bowen. The study is based on Transportation Department statistics.

With Alaska Airlines and America West in the five and six spots, respectively, United was the survey’s only top-ranked airline that is not a low fare carrier.

SkyWest, Comair, and Atlantic Southeast Airlines appeared at the bottom of the list of 16 American airlines.

Airlines generally arrived later, lost more luggage, and caused more consumer complaints in 2004 than they did the year before, the report found.

Only four of the 14 major airlines rated in both 2003 and 2004 were found to have improved – AirTran, Atlantic Southeast, JetBlue, and United.

Airline service is getting worse because more people are flying at a time when carriers have slashed their work forces, said a co-author of the study and associate professor at Wichita State University, Dean Headley.

“Morale’s going to be down and they’re not going to care if they get the bags to the loading dock in five minutes, 10 minutes, or 15 minutes,” Mr. Headley said.

The seven largest carriers, for example, employed 12% fewer people in January 2004 than they did the year before, according to the federal Bureau of Transportation Statistics.

Mr. Headley said the aviation system is also being taxed because more planes and more people are flying than they did in the two years after the September 11, 2001, attacks. However, the aviation infrastructure – runways, airport slots, and the air traffic control system – is essentially the same as it was in the delay-plagued era just before terrorists hijacked planes and flew them into buildings.

On-time performance worsened last year, with 78.3% of flights arriving on time, down from 82% in 2003. Skywest was on time the most, American Eagle the least.

The problem of deteriorating airline service came to a head over the Christmas holidays, when delays and cancellations inconvenienced more than 500,000 passengers. Regional carrier Comair canceled all its flights during the holiday weekend, and US Airways’ baggage system failed.

A report by the Transportation Department’s inspector general blamed bad weather and computer problems at Comair, and faulted poor planning and poor labor relations at US Airways.

“In a simpler system they seem to be able to do this better,” Mr. Headley said. “When it’s more taxed, the quality goes down.”

Complaints about airline service rose 27% last year, a much higher increase than the 3.3% growth in passengers. US Airways generated the most complaints, and Southwest the least.

Last year, 4.83 bags were lost, stolen or damaged for every 1,000 passengers. Atlantic Southeast had the highest rate of mishandled bags, while AirTran had the lowest.

There was a small increase in the number of passengers “bumped,” or denied boarding for space – 0.87 passengers per 10,000 boardings in 2004, up from 0.86 per 10,000 in 2003.

The report rated the 16 American airlines that carried at least 1% of the 630 million passengers who flew domestically last year. Two carriers, Comair and SkyWest, met that threshold for the first time in 2004.