Bigger isn’t always better, especially in the airline industry, but Delta Air Lines’ showing in the annual Airline Quality Rating suggests merged airlines are improving their customer performance.

Airline performance in 2013 was the highest since the Airline Quality Rating started in 1991, according to the 24th annual survey. The AQR is a joint research project funded as part of faculty research activities at Wichita State University and Embry-Riddle Aeronautical University’s Prescott, Ariz. campus.

Of the 15 carriers rated for performance in both 2012 and 2013, eight airlines improved, six airlines declined and one is new to the rankings.

The industry improved in two of the four elements of the AQR: involuntary denied boardings and customer complaints. However, performance declined in on-time performance and baggage handling in 2013.

But perhaps the most interesting item that emerged this year was Delta placing fourth on the list.

Dean Headley, associate professor of marketing at the W. Frank Barton School of Business at Wichita State University, says the strong performance by Delta shows that a large, merged airline is able to compete with the best performing smaller airline.

"Bigger hasn't always been better, but in Delta's case we are seeing a large airline perform at levels usually only seen by smaller low-fare carriers," he said.

Here are the ratings, with where the airline finished the previous year in parentheses:
1.Virgin America (1)
2.JetBlue (2)
3.Hawaiian (5)
4.Delta (4)
5.Alaska (6)
6.Endeavor (new to the rankings this year; formerly Pinnacle)
7.US Airways (9)
8.Southwest (8)
9.American (10)
10.AirTran (3)
11.Frontier (7)
12.United (14)
13.ExpressJet (13)
14.SkyWest (12)
15.American Eagle (11)

Virgin America and JetBlue remained No. 1 and 2 in 2013. Hawaiian, US Airways and United all improved two spots in the rating, to No. 3, 7 and 12 respectively. The biggest drop was AirTran from No. 3 to 10. Frontier and American Eagle each dropped four spots in the rating for 2013.

For American and United, both of which merged with US Airways and Continental, respectively, the Delta performance bodes well.

"When you look at the past 14 years, you find that the airline industry performs most efficiently when the system isn't stressed by high passenger volume and high number of airplanes in the air," said Headley. "With continued capacity limits and consolidation, one would hope that a less congested system would perform better. The challenge is whether airline performance quality improvements at this level can be maintained as more people choose to fly. Or does the infrastructure and air traffic control technology limit what the airlines can actually do?"

Brent Bowen, dean of College of Aviation at Embry-Riddle Aeronautical University, said airline operational performance is at an all-time record high, but it does not necessaril translate to customers being happy.

"Because airlines are solving operational issues and advancing in AQR elements, it is time to begin a new focus on serving travelers and expanding customer service,” he said. “These results show that airlines that intend to do better, are doing better and improving. Those losing focus have declined.”

Bowen also made mention of the pilot shortage.

"With all this good news, the flying public should be informed of and alarmed about the very real pilot shortage caused by congressional mandate and the looming personnel crisis in Air Traffic Control because of arbitrarily changing hiring rules that eliminate the most qualified applicants," he said.