Saratov Russia A mason was injured with a broken leg due to the collapse of a tower crane. The collapse was apparently caused by negligence (undisclosed) by the crane foreman. He even admitted to the negligence while being interviewed.
Looking at the picture, it appears that we have a clean separation between the turntable and mast. If this is the case, then it must have been a bolting issue. There are 8 bolts that torque up to 4300 ft lbs that and if they are not tightened properly with the counterweights over the corner being torqued or prior to going horizontal with the crane, then you will end up with bolts loosening up. If the others were pre-stressed correctly, it could be that one corner loosens up and gets a gap going unbeknown to the operator. If that gap grows, then the other have added stress and can eventually fail quickly in a zipper like fashion, one after the other.
What I used to do on bolted towers is note the position of the crane before I climbed. As I climbed I would put a hand on the bolts under compression due to the counterweights. Both corners on that side. Then when I climbed down, I would put the weights on the opposite side (wind allowing) and check the other side as I climbed down. This was a once a week operation at a minimum. It adds very little time to either climb and is simply common sense.