How foul weather and physics can turn a crane into a tragedy

It was an hour before sunset, but the holy city was already twilight dark. Late summer is Mecca’s stormy season. It’s also the season just before the hajj—Islam’s annual pilgrimage—and the Grand Mosque at the city’s center was already filled with visitors. A blustery storm was whipping through the city’s skyscrapers, half-built high rises, and thicket of tower cranes. It was probably a big gust that caught the large red and white crawler crane, pushing its massive boom like a giant lever until the machine did a backwards somersault and landed on the mosque’s roof.

When the crane hit at 5:20pm on September 11, it hit hard, and the collision shook loose tons of concrete and debris onto the pilgrims and visitors inside. One hundred and eleven are now dead, and nearly 400 injured. But cranes are for lifting big things off the ground—they’re engineered to be very, very stable. So how could one flip so disastrously?

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