In 2014, the U.S. airline industry posted its worst quality rating score in five years. Of the 12 U.S.-based carriers included in the rankings, the worst were Envoy/American Eagle, Express Jet and SkyWest with scores of -2.83, -2.12 and -1.84, respectively. No airline scored above zero.

The Airline Quality Rating (AQR) is compiled by researchers at Embry-Riddle Aeronautical University and Wichita State University from monthly data collected by the U.S. Department of Transportation. The AQR is a weighted average of 15 criteria that airline industry experts believe consumers would rate as important in judging airline quality. The criteria include on-time performance, involuntary denied boardings, mishandled baggage and a dozen items collected under the heading of customer complaints. These 12 items include flight problems, oversales and customer service.

The top-rated airline is Virgin America Inc. (NASDAQ: VA) for the third consecutive year. Virgin America scored -0.30. The airline’s on-time performance slipped slightly from the prior year to 81.5%, and it had the best score among the 12 airlines for involuntary denied boarding at 0.09 per 10,000 passengers. The customer complaint rate of 1.14 per 100,000 passengers was better than the industry average of 1.28 and the mishandled baggage rate of 0.95 per 1,000 passengers was the best among all airlines.

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Hawaiian Airlines, owned by Hawaiian Holdings Inc. (NASDAQ: HA), had the best on-time performance of any airline with a score of 91.9%, and was the second-highest ranked airline for 2014. It was one of just three airlines to post a year-over-year improvement last year. Virgin America and Alaska Airlines were the others.

Delta Air Lines Co. (NYSE: DAL) ranked third overall in 2014, though its on-time performance dropped to 83.7% and its rate of mishandled baggage rose slightly, while remaining better than the industry average. The rate of customer complaints rose year-over-year but denied boardings decreased.

The worst airline for on-time performance was Envoy Air, the renamed American Eagle airline owned by American Airlines Group Inc. (NASDAQ: AAL). Express Jet and SkyWest tied for most involuntary denied boardings with 2.71 per 10,000 passengers. Envoy also has the worst record for mishandled baggage, at 9.02 per 1,000 passengers, far ahead of second-worst Express Jet with a mishandled bag rate of 5.61. And on the basis of total customer complaints per 100,000 passengers, Frontier Airlines is the worst with an average of 3.91 in 2014.

A look at the chart from the AQR report that we have included below shows that the busiest travel times of the year generate the lowest quality scores. Complaints drop as the number of passengers thins out. There should be no big mystery here: passengers prefer a travel experience with fewer delays and lost bags and one where they get a little more service from the airlines.

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Airlines earn better returns by flying fuller and fewer planes. And the aircraft makers are giving the airlines what they want: more seats in the same amount of space, which means less leg room plus smaller restrooms and less galley space.

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