It turns out that the person who had to make the EXTREMELY DIFFICULT decision to ground air traffic across the entire country on 9/11... was on his first day on the job.
Ben Sliney (born 1945) is a former United States Federal Aviation Administration (FAA) National Operations Manager. His first day in this position was September 11, 2001, and he was responsible for ordering a National Ground Stop across United States airspace in response to the terrorist attacks of 9/11.