Originally Posted by
The Sultan
Back to the 97 it was marketed to be physically impossible for the rotors to collide due to their stiffness.
When not limiting the control throws and preventing opposite or differing blade excursions between both discs it can't really be physically impossible. Or the rotor blades would have to be so stiff that they would either break before touching or be so thick that the drag would be ridiculously high. Effectively every Helicopter can chop off his own tail if given enough cyclic authority. Control limits can possibly prevent this but that goes out off the window once control logic runs havoc which apparently was the case here.