Funny thing about the mentioned N591UA, Airframes.org has this remark about it:
Same for N644AA:w/o 2001-09-11 near Shanksville, PA, USA, 44(44). Flight UAL93 from Newark (KEWR) NJ 0847 to San Francisco (KSFO), crashed into woods at 1037. Strangely, no official NTSB accident report exists.
So.... What does this mean?w/o 2001-09-11 Arlington, VA, USA, 64(i)+125. Flight AAL77 from Washington-Dulles (KIAD) 0810 to Los Angeles (KLAX), crashed into Pentagon after diverting ER IAD-LAX at 0940. Owner USBL. Strangely, no official NTSB accident report exists.