Researchers believe the World Trade Center's south tower, though struck second on 11 September, fell first because the passenger jet that hit it had been flying about 85-90kts (155 -165km/h) faster than the other hijacked plane, according to an article in the New York Times.
The United aircraft was even at risk of breaking up in midair as it made the final turn toward the south tower, travelling at a speed far exceeding the Boeing 767-200 design limit for that altitude, a Boeing official says.
"These guys exceeded even the emergency dive speed," says Liz Verdier, a Boeing spokeswoman. "It's off the chart."
The collision speed was not the only factor – the fire was fed by thousands of gallons of jet fuel. This ultimately brought the tower down.
At a speed of about 430 knots (795 km/h), a partly-loaded Boeing 767 weighing 132,000kg would have the same energy as 750kg of TNT, according to another team of researchers at MIT.
Source: Flight Daily News
