From our office window across the river, the area behind the Pentagon is a
mishmash of woods, office buildings and Arlington Ridge, which is a minor range of hills just behind the Pentagon. (Arlington House in the national cemetary is on top of the ridge.) From our vantage, something as small as a 757 zooming along at 250-300 knots
was lost in the clutter....(the official) path has the
plane coming right at me head-on. In that orientation, a 757 would be
practically invisible, especially going 400 knots with the wheels and
flaps up. At that speed, it would have traveled from the Sheraton to
the Pentagon in just about 8 seconds, and half that time it was below
the top of the Pentagon.
That makes our sightline probably one of the
worst in the area.At 400 knots, that whole loop that Hanjour made would have lasted
about 3 minutes, and the whole time, according to the FDR chart, he
was at about 5000 feet. That would be hard to spot from my office,
even on such a clear and crisp day as Sept 11 was.
The photo on my site shows the view of the Pentagon, but it's a
telephoto shot.
http://clothmonkey.com/images/20020911%20027.jpg I've attached a normal perspective shot from the same
window, also taken on 9/11/02. You can see that spotting the plane
with the naked eye from this perspective is more of a problem.
Original:

...the (C-130) reached the Pentagon at a low altitude and made a sharp left turn, passing just north of the plume, and
headed straight for the White House.
All the while, I was sort of talking at it: "Who the hell are you? Where are you going? You’re not headed for downtown!" Ray and Verle watched it with me, and I was convinced it was another attack. But
right over the tidal basin, at an altitude of less than 1000 feet, it made another sharp left turn to the north and climbed rapidly. Soon it was gone, leaving only the thin black trail.
