When did George Tenet learn, on September 11, that a plane (or planes)
had crashed into the World Trade Center?  Some reports indicate that
he learned of the first plane crashing into WTC North Tower (see,
e.g., http://abcnews.go.com/onair/DailyNews/sept11_moments_1.html). 
Other reports indicate that he was not informed until the second
planed had crashed into the WTC South Tower. (See, e.g.,
http://www.washingtonpost.com/ac2/wp-dyn/A42754-2002Jan26)