Between September 3, 2001 and September 7, 2001: WTC Structural Engineer Says Trade Center Designed for 707 Crashing Into It

Leslie Robertson, one of the two original structural engineers for the World Trade Center, is asked at a conference in Frankfurt, Germany what he had done to protect the Twin Towers from terrorist attacks. He replies, “I designed it for a 707 to smash into it,” though does not elaborate further. [Chicago Tribune, 9/12/2001; Knight Ridder, 9/12/2001] The Twin Towers were in fact the first structures outside the military and nuclear industries designed to resist the impact of a jet airplane. [Robertson, 3/2002; Federal Emergency Management Agency, 5/1/2002, pp. 1-17] The Boeing 707 was the largest in use when the towers were designed. Robertson conducted a study in late 1964, to calculate the effect of a 707 weighing 263,000 pounds and traveling at 180 mph crashing into one of the towers. He concluded that the tower would remain standing. However, no official report of his study has ever surfaced publicly. [Glanz and Lipton, 2004, pp. 138-139, 366] A previous analysis, carried out early in 1964, calculated that the towers would handle the impact of a 707 traveling at 600 mph without collapsing (see February 27, 1993). In 2002, though, Robertson will write, “To the best of our knowledge, little was known about the effects of a fire from such an aircraft, and no designs were prepared for that circumstance.” [Robertson, 3/2002] The planes that hit the WTC on 9/11 are 767s, which are almost 20 percent heavier than 707s. [Scientific American, 10/9/2001; New Yorker, 11/19/2001]