updated 5/12/2006 11:43:23 AM ET 2006-05-12T15:43:23

The number of airline flight delays in April was 31 percent higher than the same month last year, thanks mostly to a thunderstorm pattern that could mean trouble ahead for summer travelers, the head of the Federal Aviation Administration said Thursday.

The severe storms typical of summer arrived earlier this year and with greater frequency, said Marion Blakey.

"That doesn't bode well" for the coming months, she said in an Associated Press interview.

At the 35 busiest airports, through which almost all passengers travel, the number of delays rose to 922 in April from 704 during the same month last year.

The FAA expects planes to be more crowded than ever this summer. Passenger volume is rising again following a drop after the attacks of Sept. 11, 2001.

At the same time, the number of flights is dropping — from 44,000 in April 2005 to 42,000 a year later — as airlines try to save on jet fuel and trim costs by flying fewer airplanes.

The sheer number of travelers will make it harder to deal with delays and cancellations, Blakey said, because airlines have fewer empty seats in which to put stranded travelers.

For the past two years, her agency has monitored delays closely from its Air Traffic Control System Command Center in Herndon, Va., keeping planes on the ground at smaller airports so large airports can clear away backed-up traffic.

This results in more and smaller delays, but the aviation system as a whole functions better, Blakey said.

"It's a plan and an approach that for the last two years has worked well with big airports and I think we're going to see us expanding that," Blakey said.

The plan seemed to work in April. Though more flights were late, the average length of delay in April was 44 minutes, three minutes shorter than the 47-minute average for the first four months of the year, according to FAA data.

Hot muggy air produces thunderstorms, usually in a zone from Texas to Michigan. The storms are too high to fly over, too dangerous to fly through and often too wide to fly around.

At major airports — especially Chicago's O'Hare — bad weather can combine with huge numbers of passengers to cause delays that cascade through the entire aviation system. That is what happened during the summer of 2000, when thousands of passengers slept on terminal floors or fumed while their planes waited on runways.

Blakey had two pieces of advice for summer traveler: Book flights that take off early in the day because thunderstorms tend to develop in the afternoon and leave plenty of time to get to the airport.

Blakey said aviation safety has improved in the past decade. Ten years to the day after ValuJet Flight 592 plunged into the Everglades and killed 110 people, she said that aviation has never been safer. There is now one fatal accident for every 5 million takeoffs and landings, she said.

She also said financial problems among airlines will not tempt the government to emulate Europe's pattern of regulating airport access and restricting routes.

European airlines are in better financial shape than their counterparts in the U.S., where there is more demand and fiercer competition, she said.

"I would not anticipate anything where we go back to the long arm of government setting up routes and, in effect, determining a lot of the economic course of the industry," Blakey said.

The intense competition in the U.S. aviation market is a result of deregulation, which took place in 1978.

"That level of competition has certainly brought on real problems for the upper tier," Blakey said, alluding to such traditional airlines as United, US Airways, Delta and Northwest. United and US Airways emerged from bankruptcy in the past year; Delta and Northwest are now under bankruptcy protection.

Blakey predicted more airlines will merge and some aggressive low-cost startups will go out of business, as Independence Air did in January.

Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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