I sure would like to see that video in slo-mo.
It looks like the top is swivelling in the wind. That swivelling, along with the blades moving at such high speed, would put an awful lot of torque on the main shaft or on the bolted ends of the blades. At that speed, once one bolt failed (if that's what happened), the whole thing was doomed. I can't tell if it was a blade that failed, or if it was the main shaft in the top housing. Regardless, those blades were likely being deformed from their intended shape under those conditions, resulting in some pretty severe shear stresses.
Yeah, those systems are supposed to be computer controlled to automatically adjust the blade pitch under different wind speeds to optimize their power output and also avoid catastrophic failure. As with anything, the weakest part can bring the whole thing down.
I've passed trucks carrying those blades on the Interstate. They're enormous.
Kevin...
