In an attempt to communicate with Flight 11's cabin, hijacker Mohammed Atta mistakenly contacts air traffic control. Minutes later, he makes a second unintended transmission to ground control.1

1 “Hijacker Transmission” National September 11 Memorial & Museum n.d. Web. March 16, 2011 http://timeline.national911memorial.org/#/Explore/2/AudioEntry/551
Courtesy of the National 9/11 Memorial and Museum