(CNN) -- Under pressure from Congress, NASA on Monday released thousands of pages of complaints from pilots about crew fatigue, air traffic congestion and communications.
NASA Administrator Michael Griffin has questioned the validity of the study that revealed problems with air traffic.
The findings, some of which were leaked in October but not officially released until now, include reports of twice as many bird strikes, near-midair collisions and runway incursions than current government monitoring systems show.
The aerospace agency's chief called raw data from the controversial air-safety research program unreliable and left analysis up to aviation safety experts.
None of the data "should be viewed or considered at this stage as having been validated," NASA Administrator Michael Griffin told reporters in a conference call Monday afternoon.
The findings include surveys of more than 30,000 commercial and private pilots, conducted primarily from 2001 to 2004.
Results of the study, which cost the space agency about $1 million a year to conduct, will be turned over to the National Academy of Sciences and aviation safety experts to analyze, Griffin said.
"What the public should understand is that they have approximately the same risk from dying from a lightning strike as they do from dying in an air transport accident in the United States," said Griffin.
He said accounts of engine failures being up to four times higher than previously reported in Federal Aviation Administration reports "call into question the reporting mechanism."
"The fundamental concern I had at the time of my testimony and still have is that this research work was not properly peer reviewed at its inception, and the data extracted from the survey was not properly validated at its conclusion," Griffin said.
Members of Congress, aware of the findings in October, pressured Griffin to release the information to the public.
"That is all that we have ever, in fact, been asked for, is to release the data, and it is all that we have ever promised," he said Monday.
The agency's earlier refusal, he said, "left the wrong impression."
Experts who designed and conducted the study defended it during an October hearing of the House Science and Technology Committee.
Robert Dodd, the principal investigator on the study for seven years, said he was "disappointed and perplexed" when he learned NASA initially would not make the findings public. E-mail to a friend 
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