I don't get the point of this article. Is the author trying to say that airplanes didn't hit the Towers? If so, where did the missing airplanes go? Were all the eyewitnesses in New York hynotized en masse?

Sorry, airplanes hit the Towers.

OK, maybe the author is trying to say that the plane hits couldn't bring down the Towers. As evidence of this, he presents a mishmash of anecdotes and suppositions, none of which are very convincing. He certainly doesn't present a critical framework in favor of his case, not surprising since he has no qualifications in the subject. He's a Professor Emeritus but not an engineer, let alone a structural or metallurgical engineer who might actually know something about this unique case. Apparantly he's some sort of retired economist.

As it happens, I am an engineer, a metallurgical engineer. The professional journal of TMS, Journal of Metals, devoted an issue to the mechanism of the Towers' collapse several months after 9-11. I don't recall all the details and must admit that my eyes glazed over in the middle of some of the articles but the mechanisms behind the structural failures were discussed in detail and were convincing.

Briefly, the impact of the airplanes, their kinetic energy, was far too small to knock down buildings of that size or even make them sway much. These things were designed to take lateral loads from hurricanes.

The jet fuel burn, in itself, couldn't cause the collapses either: it burned too fast and was gone in a very few minutes.

What the jet fuel could do was ignite the enormous amount of paper in all the filing cabinets and bookshelves in all those offices, creating a fire that could burn long enough and hot enough to heat the building joints. These were designed with insulation to withstand fires, to be sure, but the protective insulation of some was damaged or destroyed by the crash so they were naked to the heat. They weren't designed for that and gradually weakened until one failed. That shifted more load to its weakened neighbors so that they failed, shifting their combined loads to their neighbors, weakened or not, and they failed. Etc.

The joints failed in series like a zipper ripping open until a floor collapsed, dropping a shock load on the floor below it so that it collapsed too and down came the Towers.

The Towers were not merely expanded versions of other, smaller buildings. They were a unique design and any experienced engineer can tell you that very large, cutting-edge designs often display quirks and flaws that no one spots until it's too late. The Towers were designed to withstand hits from 707s; planes as big as the 9/11 jets weren't on the drawing boards when the Towers were designed in the 1960s. It's possible anyway that nobody considered the combined effects of damaged joint insulation coupled with an unfightable fire.

In fine: 1)Planes hit the Towers. 2) The impacts damaged critical insulation on some of the structural components. 3) Simultaneously, the fuel explosions triggered severe paper/wood fires in the building offices. 4) Heat from the fires weakened the now-naked building components (joints) to the point of failure. 5)The initial failures triggered a chain reaction of structural failures. 6) The Towers came down.

No conspiracy theories are needed to explain this aspect of the 9/11 tragedies.