Aircraft impact Design for Twin Towers


New Member
I was reading on Wikipedia about the design for the Towers. It said the following " In designing the World Trade Center, Leslie Robertson considered the scenario of the impact of a jet airliner, the Boeing 707, which might be lost in the fog, seeking to land at JFK or at Newark airports ".

Does anyone have documentation to indicate this ? I'm inclined to believe it, as no building can withstand an impact from a plane traveling at high speed and full of fuel. Just look @ the pentagon for example.
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Senior Member.
NIST says ( I added bold emphasis)
page 55


New Member
I heard about that, and I find it hard to believe they could design the building to take that sort of impact. Not even the pentagon, which is reinforced was able to hold up to an impact.


Senior Member.
I'm inclined to believe it, as no building can withstand an impact from a plane traveling at high speed and full of fuel.
The WTC withstood the impact for hours an hour as is. Mechanically, the engineering was sound. What brought it down were the fires.

If an analysis was done, it might not have considered the consequences that this kind of fire might have. A "seeking to land" airliner would not be "full of fuel", as it would be near the end of their journey.
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Senior Member.
Not even the pentagon, which is reinforced was able to hold up to an impact.

the Pentagon didn't collapse. there was just a big hole, like the Twin towers.

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Keith Beachy

Senior Member
The structural engineer designed the tower for an impact of a 707 lost in the fog trying to land, it would be at 180 to 200 mph.

The two towers were the first structures outside of the military and nuclear industries designed to resist the impact of a jet airliner, the Boeing 707. It was assumed that the jetliner would be lost in the fog, seeking to land at JFK or at Newark. 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. Indeed, at that time, no fireproofing systems were available to control the effects of such fires.

It appears that about 25,000 people safely exited the buildings, almost all of them from below the impact floors; almost everyone above the impact floors perished, either from the impact and fire or from the subsequent collapse. The structures of the buildings were heroic in some ways but less so in others. The buildings survived the impact of the Boeing 767 aircraft, an impact very much greater than had been contemplated in our design (a slow-flying Boeing 707 lost in the fog and seeking a landing field). Therefore, the robustness of the towers was exemplary. At the same time, the fires raging in the inner reaches of the buildings undermined their strength. In time, the unimaginable happened . . . wounded by the impact of the aircraft and bleeding from the fires, both of the towers of the World Trade Center collapsed.

To add to the speculation there was a "white paper" (a marketing device) by the Port Authority to brag about the WTC towers, and it had a 707 at 600 mph... I think Robertson wanted to stop the 707 at the shell. With the planes on 9/11 going 470 and 590 mph, they broke the shell. The buildings did not collapse due to the impacts. This was an issue since a plane had hit the Empire State Building. There was no study of an impact at 600 mph - it appears to be Port Authority marketing, not an engineering study.

At 180 mph the shell of the WTC would stop the aircraft at the shell. There was a study after 9/11 of what it would take to break the shell, and what thickness of steel could stop the 590 mph impact... Have to look it up -

The most likely accident with an aircraft and building would be lost in the fog low on fuel trying to land. If the pilot had full fuel he would (if he had any judgement) climb to VFR (clear sky) and find suitable landing field.

Found the paper... I have a copy on a computer at home.
A numerical simulation of the aircraft impact into the exterior columns of the World Trade Center (WTC) was done using LS-DYNA. For simplification, the fuselage was modeled as a thin-walled cylinder, the wings were modeled as box beams with a fuel pocket, and the engines were represented as rigid cylinders. The exterior columns of the WTC were represented as box beams. Actual masses, material properties and dimensions of the Boeing 767 aircraft and the exterior columns of the WTC were used in this analysis. It was found that about 46% of the initial kinetic energy of the aircraft was used to damage columns. The minimum impact velocity of the aircraft to just penetrate the exterior columns would be 130m∕s. It was also found that a Boeing 767 traveling at top speed would not penetrate exterior columns of the WTC if the columns were thicker than 20mm.
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I don't see that claim anywhere on the current Wikipedia page for the World Trade Center.

And saying "... no building can withstand an impact from a plane traveling at high speed and full of fuel ..." is vague and probably overly broad. Absolutes rarely exist without exceptions. For instance, in 1945 a B-25 bomber crashed into the Empire State Building and it survived.

This one has been analysed to death. The key difference being that the B-25 was comparitively small and slow. The maximum speed of a B-25 is 272mph, for instance, which makes a huge difference in the kinetic energy.

Absolutely agree that the statement is uselessly vague, haha.


Senior Member
The best accounting of the Port Authority's study of a 707 impact at 600 mph can be found in James Glanz's book "City in the Sky". I found it first in this 2011 post at the JREF forum by user "tfk":

Earlier this year, I read the book myself, I have a copy, and checked that the quotes and page numbers given by tfk are correct. Here are the technical excepts from Glanz's book as far as tfk has them:
In the book, the story is layed out on pages 131 thru about 139.
I think it is best if you read tfk's full post for context and explanation.


Senior Member.
More from the forum post that Oystein cites:
The second calculation imagined that a number of the beams on one side of the building, equivalent to the wingspan of the plane, were "surgically removed". As if you just took a Sawzall & cut them out. Absolutely no other damage to any part of the building. No fires, no damaged core columns, no damaged floors, etc.

The question asked: Would the building fall over under this condition.

They found out that it would not.

Clearly, neither one of these very unrealistic & very crude calculations comes anywhere CLOSE to a rigorous analysis upon which one could make the assertion that the building "was designed to withstand a jet impact".

So, yes, a crude (?) impact analysis, but no postcrash considerations, it seems.
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