U.S. airlines plan to fly planes full this summer and wait out delays caused by weather and congestion rather than cancel flights, the nation's top aviation regulator said Thursday.

Domestic carriers anticipate flying an estimated 200 million passengers between now and the beginning of September with low fares pumping up passenger volume and traffic.

In a departure from previous practice, airlines are not expected to keep significant backup aircraft on hand to respond to big delays during the summer travel season, said Marion Blakey, the Federal Aviation Administration (search) administator. "We will have controllers in place," Blakey said.

Delays cost airlines more than $6.2 billion in operating expenses in 2004, industry figures show. Flights are considered delayed when they are more than 15 minutes late.

Airline delays are usually worse in summer than the rest of the year because of thunderstorms, and Blakey said national weather forecasters are predicting a heavy storm season.

"We're doing everything we can to get ready for the traffic and the weather," Blakey said after a Senate Commerce subcommittee hearing.

Transportation Department (search) figures show more than a quarter of flights by domestic airlines were delayed in the first three months of 2005, a 17 percent increase over the same period last year.

The average delay was 52 minutes compared to 48 minutes for the same period in 2000, the worst year ever for on-time performance. Commercial takeoffs and landings nationwide in April exceeded operations for the same month five years ago by 4 percent.

The trend has followed a rebounding in traffic in the past two years.

The number of passengers jumped from 642 million in 2003 to 688 million last year. This year's summer projection of 200 million is 4 percent higher than last year, according to the industry's chief trade group, the Air Transport Association (search).

Weather accounts for 70 percent of fight delays, but transportation officials say greater competition between legacy and discount airlines -- especially in the East -- as well as heavier regional jet use are driving up wait times.

Twelve of the top 15 airports for delays have had traffic growth this year. Up to one-in-three flights are delayed at New York's LaGuardia, Philadelphia, and Newark. But delays are not limited to the busiest destinations. For example, the top two airports for delays are West Palm Beach (40 percent of flights) and Ft. Lauderdale, Florida (37 percent).

While transportation officials have historically pointed to weather and airlines as delay causes, industry has long been critical of an aging FAA air traffic control system and airspace management.

"The system was already creaking back in (2001). We're back to pre-(Sept. 11) traffic and as a result of that we're seeing the same problems we saw before," David Cote, chief executive of Honeywell International Inc. said Wednesday.

Congressional investigators at the Government Accountability Office (search) have concluded the FAA's primary air traffic modernization program will not be able to keep pace with future demand. The FAA says some airports may not keep up but controllers should be able to manage traffic systemwide.