NASA gathered the information under an $8.5 million safety project, through telephone interviews with roughly 24,000 commercial and general aviation pilots over nearly four years. Since ending the interviews at the beginning of 2005 and shutting down the project completely more than one year ago, the space agency has refused to divulge the results publicly.
Just last week, NASA ordered the contractor that conducted the survey to purge all related data from its computers.
The Associated Press learned about the NASA results from one person familiar with the survey who spoke on condition of anonymity because this person was not authorized to discuss them.
A senior NASA official, associate administrator Thomas S. Luedtke, said revealing the findings could damage the public's confidence in airlines and affect airline profits. Luedtke acknowledged that the survey results "present a comprehensive picture of certain aspects of the U.S. commercial aviation industry."
The AP sought to obtain the survey data over 14 months under the U.S. Freedom of Information Act.
"Release of the requested data, which are sensitive and safety-related, could materially affect the public confidence in, and the commercial welfare of, the air carriers and general aviation companies whose pilots participated in the survey," Luedtke wrote in a final denial letter to the AP. NASA also cited pilot confidentiality as a reason, although no airlines were identified in the survey, nor were the identities of pilots, all of whom were promised anonymity.
Among other results, the pilots reported at least twice as many bird strikes, near mid-air collisions and runway incursions as other government monitoring systems show, according to a person familiar with the results who was not authorized to discuss them publicly.
The survey also revealed higher-than-expected numbers of pilots who experienced "in-close approach changes" - potentially dangerous, last-minute instructions to alter landing plans.
Officials at the NASA Ames Research Center in California have said they want to publish their own report on the project by year's end.
"If the airlines aren't safe I want to know about it," said Rep. Brad Miller, D-N.C., chairman of the House Science and Technology investigations and oversight subcommittee. "I would rather not feel a false sense of security because they don't tell us."
Discussing NASA's decision not to release the survey data, the congressman said: "There is a faint odor about it all."
Miller asked NASA last week to provide his oversight committee with information on the survey and the decision to withhold data.
"The data appears to have great value to aviation safety, but not on a shelf at NASA," he wrote to NASA's administrator Michael Griffin.
The survey's purpose was to develop a new way of tracking safety trends and problems the airline industry could address. The project was shelved when NASA cut its budget as emphasis shifted to send astronauts to the moon and Mars.
NASA said nothing it discovered in the survey warranted notifying the Federal Aviation Administration immediately. Its data showed improvements in some areas, the person who was familiar with the survey said. Survey managers occasionally briefed the FAA during the project. At a briefing in April 2003, FAA officials expressed concerns about the high numbers of incidents being described by pilots because the NASA results were dramatically different from what FAA was getting from its own monitoring systems.
An FAA spokeswoman, Laura Brown, said the agency questioned NASA's methodology. The FAA is confident it can identify safety problems before they lead to accidents, she said.
In its space program, NASA has a deadly history of playing down safety issues. Investigators blamed the 1986 and 2000 shuttle disasters on poor decision making, budget cuts and improperly minimizing risks. NASA decided to go ahead with a 2006 shuttle launch and is moving ahead with one this week despite safety concerns by NASA engineers in both cases.
Aviation experts said NASA's pilot survey results could be a valuable resource in an industry where they believe many safety problems are underreported, even while deaths from commercial air crashes are rare and the number of deadly crashes has dropped in recent years.
"It gives us an awareness of not just the extent of the problems, but probably in some cases that the problems are there at all," said William Waldock, a safety science professor at Embry-Riddle Aeronautical University in Phoenix, Ariz. "If their intent is to just let it sit there, that's just a waste."
Officials involved in the survey touted the unusually high response rate among pilots, 80 percent, and said they believe it is more reliable than other reporting systems that rely on pilots to voluntarily report incidents.
"The data is strong," said Robert Dodd, an aviation safety expert hired by NASA to manage the survey. "Our process was very meticulously designed and very thorough. It was very scientific."
Pilot interviews lasted about 30 minutes, with standardized questions about how frequently they encountered equipment problems, smoke or fire, engine failure, passenger disturbances, severe turbulence, collisions with birds or inadequate tower communication, according to documents obtained by the AP.
Pilots also were asked about last-minute changes in landing instructions, flying too close to other planes, near collisions with ground vehicles or buildings, overweight takeoffs or occasions when pilots left the cockpit.
The survey, known officially as the National Aviation Operations Monitoring Service, started after a White House commission in 1997 proposed reducing fatal air crashes by 80 percent as of this year. Crashes have dropped 65 percent, with a rate of about 1 fatality in about 4.5 million departures.
NASA had begun to interview general aviation pilots and initially planned to interview flight attendants, air traffic controllers and mechanics before the survey was halted.
In earlier interviews that helped researchers design the NASA survey, pilots said airlines were unaware how frequently safety incidents occurred that could lead to serious problems or even crashes, said Jon Krosnick, a survey expert at Stanford University who helped NASA create the questionnaire. Krosnick also led a Stanford team that paid for a joint AP-Stanford poll on the environment.
"There are little things going on everyday that rarely lead to an accident but they increase the chances of an accident," said Krosnick. "It's the little things beneath the surface that cause the very infrequent crashes. You have to tackle those."
NASA directed its contractor Battelle Memorial Institute, along with subcontractors, on Thursday to return any project information and then purge it from their computers before Oct. 30.