8:46:26: Flight 11 crashes at roughly 466 mph (790km/h or 219m/s or 425 knots) into the north face of the North Tower (1 WTC) of the World Trade Center, between floors 93 and 99. (Many early accounts gave times between 8:45 and 8:50). The aircraft enters the tower mostly intact.
It plows to the building core, severing all three gypsum-encased stairwells, dragging combustibles with it. A powerful shock wave travels down to the ground and up again. The combustibles and the remnants of the aircraft are ignited by the burning fuel. As the building lacks a traditional full cage frame and depends almost entirely on the strength of a narrow structural core running up the center, fire at the center of the impact zone is in a position to compromise the integrity of all internal columns. People below the severed stairwells start to evacuate—no one above the impact zone is able to do so.
10:28:25: The North Tower of the World Trade Center begins to collapse.
Due to the destruction of the gypsum-encased stairwells on the impact floors (most skyscraper stairwells are encased in reinforced concrete), no one who was above the impact zone in the North Tower escapes the collapse. The Marriott Hotel, located at the base of the two towers, is also destroyed. The second collapse is also viewed live on television and heard on radio. The North Tower collapses 1 hour, 41 minutes and 45 seconds after the impact of Flight 11.
Several long-distance videos of the collapse, such as CNN, were able to notice that, after the cloud of dust had partially cleared away, a portion of the building was still standing. It appeared to be the lower half of the northwest corner column of the North Tower, which, like a spire, grew larger and had more structure still standing near the bottom. The portion rose to a fairly good height considering the collapse around it, as it appeared to rise nearly forty stories off the ground. This piece remained standing for a few seconds after the initial collapse before it also came down.
