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.
Although to most people NASA is associated with spaceflight, the agency has a long and storied history of aviation safety research. Its experts study atmospheric science and airplane materials and design, among other areas.
"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."