My friend who saw the low-flying plane over Washington last night was kind enough to email his full description of what exactly he witnessed. Note my original item was wrong about the time of the sighting:
As planes were belatedly descending into Ronald Reagan Airport at around 1:15 AM, all of a sudden a big plane appeared over the National Cathedral, banking slightly left and rapidly moving towards Massachusetts Avenue right in the direction towards the White House.
I could see that very clearly, since I was just going to write my daily memo to my editor, and my desk faces West/Northwest on 22nd Street in the direction of Cathedral Heights, on the uppermost (tenth) floor. It's a great view.
The plane descended further and banked to the right approximately over Kalorama, at about 150-200 yards altitude. I had already jumped to my feet and was leaning out the window, when the plane sharply and noisily accelerated, getting beyond my point of view over the rooftop of my building. It was either a Boeing 737 or an Airbus 321, most probably Boeing, and it was flying right over Mass Av/Phillips Collection at that point of time.
I ran onto my balcony, facing P looking south, expecting the plane coming into view again over Dupont Circle, but that did not happen. It had obviously turned northeast in a frenzied angle. I heard the noise fade and disappear quickly.
Guess the pilot had mistakenly followed Rock Creek Park Valley, thinking he'd been over the Potomac Valley all the time.
That plane came probably within mere seconds of being taken down with the missiles on top of the New Executive Building. This was the closest ever a low-flying big civil plane got to the White House thus far. Even on 9/11, the Pentagon plane was much farther away from it than this one.
4 hours ago