An overall ranking of the 17 airlines based on their combined performance in four categories was to be released Monday.

The improved performance was not surprising because 2007 was the worst year for airlines in the study, said co-author Dean Headley, an associate professor of marketing at Wichita State.

The aviation system suffered close to a meltdown in 2007 as domestic carriers reported 770 million passengers in the busiest year for air travel since before the attacks of Sept. 11, 2001. Aviation experts said the air transport system had reached capacity.

There were 741 million passengers in 2008, and airlines are reporting weak travel demand through the first quarter of this year,

"We're now in a time when the system is constricting and performing reasonably well," Headley said. He urged Congress to take advantage of this "breathing room" to move forward on a system that would replace decades-old radar technology with satellite-based technology.

That new system is forecast to increase air transportation system capacity by enabling planes to fly closer together and more directly to their destinations, saving time and fuel.

"It's crazy to think we can keep going the way we were going with the volume of planes we have in the air," Headley said.