An unprecedented national survey of pilots by [NASA] has found that safety problems like near collisions and runway interference occur far more frequently than previously recognized. But the government is withholding the information, fearful it would upset air travelers and hurt airline profits. NASA gathered the information ... through telephone interviews with roughly 24,000 commercial and general aviation pilots over nearly four years. Since shutting down the project more than one year ago, the space agency has refused to divulge its survey data publicly. Last week, NASA ordered the contractor that conducted the survey to purge all related data from its computers. Congress on Monday announced a formal investigation of the pilot survey and instructed NASA to halt any destruction of records. A senior NASA official, associate administrator Thomas S. Luedtke, said earlier that 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. 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. 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. 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.

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