911

Snopes.

***

According to Hyman Brown, a University of Colorado civil engineering professor and the World Trade Center's construction manager, 1 and 2 World Trade Center were designed to survive an impact and resulting fires from a collision by the largest commercial aircraft at the time, a Boeing 707-340.

versus

Why Did the World Trade Center Collapse? Science, Engineering, and Speculation

and

It wasn't until Dr. Thomas Eagar saw Building 7 of the World Trade Center implode late on the afternoon of September 11th that he understood what had transpired structurally earlier that day as the Twin Towers disintegrated.