Nasa attacked on air safety study
A survey of air safety by the US space agency, Nasa, has come in for criticism from members of Congress.
The 16,000-page document has been presented in a way that makes it difficult to analyse, members of Congress have said.
Nasa has also been criticised for releasing only parts of its findings on New Year's Eve - an attempt, critics say, to bury the report.
Researchers interviewed nearly 30,000 pilots about their experiences.
The data shows that there were hundreds of cases where pilots flew too close to other planes, plunged from altitude or landed at airports without clearance.
The head of Nasa, Michael Griffin, said the public should not be worried about the findings, but congressmen said they needed further study.
The federal air safety study had previously been withheld from the public over concerns it would upset travellers and hurt the commercial interests of the airlines, correspondents say.
Brad Miller, a Democratic member of Congress, said the report was out of date and vowed to press Nasa further on the issue.
"This is now three years old, and it's been dumped, unanalysed and scrubbed of much of the useful information," he said.
Delivering the study, Nasa chief Michael Griffin said: "It's hard for me to see any data here that the travelling public would care about or ought to care about."
Mr Griffin said Nasa had never intended to analyse the data it collected, but planned to pass its methodology of the study to the US aviation community.
He denied the report was intentionally published on New Year's Eve to bury its findings.