"It may be the leading problem," Mitchell said.
Travel and fare expert Terry Trippler released an analysis Thursday comparing what flights airlines offer in certain markets and how many seats they involve. For example, from Minneapolis/St. Paul to Newark, Northwest Airlines has five flights a day, compared with six for Continental, but Northwest can carry 226 more passengers on its larger jets.
Continental responded that it has made an effort to change the planes it uses so it can grow without adding flights in Newark. For example, Continental carried 9 percent more passengers in August than it did last year without adding a flight, Messing said.
Last week it announced it will be adding more than 50 flights in Cleveland. Continental said many of the planes in Cleveland will be smaller regional jets it had been flying in Newark.
Another option that's been discussed is congestion pricing, where ticket prices for flying at the most popular time of day would be higher, Mitchell said.
The airlines also could be forced to point out when flights are chronically late.
One problem facing airlines now is they don't want to make sacrifices, such as slowing their growth, if their rivals don't do the same.
But cooperative efforts are often forbidden under laws designed to ensure competition. For example, if they all raised fares during peak demand times, they might be able to reduce the number of flights, but carriers are not allowed to talk to each other about pricing.
More horror stories
The number of domestic passengers is expected to rise to more than 1 billion a year by 2015, according to FAA estimates.
Those estimates prompted Mitchell to say that the problems that resulted in horror stories about passengers who got stuck for hours inside jets parked on ramps this year will only get worse.
The airlines have put much of the blame for delays on the FAA and the air traffic control system, which they say has not kept up with the airline business's growth.
The FAA earlier this month announced a redesign of the New York, New Jersey and Philadelphia metropolitan areas' airspace. Those changes in the routes used for landing and takeoffs are expected to reduce delays.
That was hailed by the chief of the Air Transport Association, James May, who called it a long-awaited first step to relieve "unprecedented" congestion in the Northeast.
The FAA also has a long-term plan to upgrade the air transport control system, but it needs support in Congress to pay for the costly project.
The tax system that funds the FAA and the authority for its programs both expire Sept. 30. The FAA is pushing "NextGen," short for the Next Generation Air Transportation System Financing Reform Act of 2007. It says the NextGen system will accommodate two to three times current traffic levels, but a fight is expected over how to pay for it.
Aviation consultant Mike Boyd of the Boyd Group said he thinks that the government largely is responsible for what is happening with the nation's air traffic system.
"Unfortunately, instead of the DOT investigating why the FAA has failed, they are investigating the airlines, which are just trying to meet the needs of the nation," Boyd said.
The FAA is seven years late in its program to update the air traffic control system and five times over budget, Boyd said.
"It is outrageous," Boyd said. "This is a smokescreen of the worst kind."
Aimed at 4th of July congestion around New York airports
Thousands of new air traffic controllers are needed to alleviate flight congestion delays in the New York-New Jersey metropolitan region and nationwide, officials representing the controllers union...
462 jets sat on runways three or more hours
Notably, 5 of 8 flights between RIC and JFK are among the most delayed.