Flying may be riskier than once thought, according to a survey of flying conditions in the U.S. carried out for NASA, the space agency.

NASA has refused to release the full report, saying it could undermine passenger confidence in the airline industry, but officials have leaked its key findings to themedia.

The report was based on a four-year project that interviewed over 24,000 commercial and general aviation pilots in the U.S. NASA ended the project more than a year ago. According to news reports, the survey found that pilots reported “twice as many bird strikes, near midair collisions and runway incursions as other government monitoring systems show.” Furthermore, the survey also found that there were “higher-than-expected numbers of pilots who experienced ‘in-close approach changes’ – potentially dangerous, last-minute instructions to alter landing plans.”

This contrasts with data collected by the aviation industry available here that indicate a rapid improvement in flight safety both in the US and around the world. Industry data indicating a decrease in accident rates are accurate because they reflect actual plane crashes, however, they do not count near-misses or indicate broader risk environments in the US or other countries.

The U.S., which accounts for about 40 percent of world air travel, has seen a 65 percent drop in its accident rate in the last ten years. It had just one fatal accident in about 4.5 million flights through September 2007, a big improvement from one death for every 2 million flights in 1997. The International Air Transport Association, the airlines’ main lobby group, reported 12 fatal accidents through July last year, compared with 20 in all of 2006 and 26 in 2005. 

Washington-based Flight Safety Foundation says release of NASA’s data would help advance “the work on reducing runway incursions, bird strikes and near mid-air collisions.” It said, “the NASA report may change the magnitude of the problem, but not the basic problem itself.” 

FSF Executive Vice President Bob Vandel commented that analysts in the US are no longer restricted to collecting flight safety data from accident sites and black boxes. He said that they can now draw data “from ‘normal’ operations and minor incidents and catch problems before the tragedy of a crash.”