Today afternoon at around 2.00 p.m. I heard the sound of a plane very close to our building. It sounded as if the plane was heading towards our building. I work at 20th floor. Almost all my friends in the floor got kinda jittery and started to look at the window. But we couldn't see anything. One of my friend told he saw a B-2 bomber flying just on top of our building. Another friend told that he saw a fighter plane, more like an F-16. Then at the same time the alarm went on for building evacuation. Even thought it was a routine evacuation drill, and we were announced about this drill a week before, the timing made it really look like a real evacuation.whew... what a day!