The idea behind the NASA aviation safety program was simple -- ask those who work in the system day in and day out about safety-related incidents and then use the information to reduce accidents.
NASA surveyed some 24,000 commercial and general aviation pilots over nearly four years, but the data, collected through early 2005, have never been released. Just six days ago, those affiliated with the project got an e-mail, asking them to turn over any data to NASA and delete survey information from their personal computers.
Jon Krosnick of Stanford University, who helped develop the pilot survey, said it could have made the skies safer.
"Why then, given that benefit, would the government prefer to shut the program down?" Krosnick told ABC News. "Well, certainly one possibility -- that the rates of events are in some cases are higher than people might expect."
The program, called the National Aviation Operations Monitoring Service, grew out of a government goal to reduce aviation accidents by 80 percent over 10 years. That goal was set in 1997 by an aviation commission chaired by then Vice President Al Gore.
NASA spent at least $8.5 million to design and conduct the survey.
The questionnaire covered dozens of safety issues including runway incursions, near misses and engine failure. One source affiliated with the project said it was turning up many more reports of incidents than were officially reported to the FAA.
"There's no question the FAA did not want this out in any way, shape or form," that source told ABC News.
The FAA denies this.
"We are always interested in safety data and the analysis and mining of aviation safety data," FAA acting administrator Bobby Sturgell said.
Sturgell said the FAA also questioned the survey methodology.
"You could not tell where the data came from, and you could not tell if it was the same event being reported on [twice,]" Sturgell said. "There were a number of things which would not enable you to analyze the data and come up with valid actions based on it."
But Krosnick said no one previously questioned the validity of the data.
"There was a lot of testing in advance," he said," to make sure the questionnaire was designed appropriately, that we would get high response rates, and that we would be able to get accurate and honest reports from pilots."
The Associated Press said it had been trying, unsuccessfully, to get the data released through a Freedom of Information Act request.
Just how sensitive the information is seems clear in a document from NASA denying that FOIA request. NASA said "release of the data ... could materially affect the public confidence in, and the commercial welfare of, the air carriers."
The union representing the majority of commercial pilots in the United States said the program is tremendously valuable. "What good is information unless we're able to analyze it and use it? Were some people trying to hide from this?" Captain John Prater, president of the Air Line Pilot's Association, asked.
Members of Congress have now demanded that the data be preserved and presented to lawmakers.