The Federal Aviation Administration (FAA) systems failed on early Wednesday morning. This accident that ＿＿（11）＿＿ thousands of flights across the country appeared to have been the result of a mistake. According to the internal review, an error occurred during the routine ＿＿（12）＿＿ . "An engineer replaced one file with another, not realizing that the mistake was ＿＿（13）＿＿ made," an official said. As the systems began showing problems and ＿＿（14）＿＿ failed, FAA staff feverishly tried to figure out what had gone wrong. The engineer who made the error did not realize what had happened. The FAA said normal operations were ＿＿（15）＿＿ gradually after ordering a nationwide pause on all domestic departures. It regretted that a computer failure had delayed and canceled flights around the country.