I saw this three years ago and then never found it again, although I've often thought about it. Seeing the picture surrealestate posted this morning got me to actually search for this post:
Here is my post from the first anniversary (I didn't have this journal in September of 2001):
Just yesterday, completely independent of thoughts about the anniversary, I saw an airplane and thought about it crashing into a building. Even after four years, that's still what airplanes do.