Originally Posted by
SansAnhedral
Occam's razor suggests more and more this was likely an issue with the VH blades and their well documented, however poorly explained and understood, vertical hop phenomenon - between the noticeable tail wag at ground idle of the accident aircraft before the incident, to the flight envelope at the moment of the incident, to the condition of the rotor system at recovery.
Just to add, the same "vertical hop" and tail wag are possible with Bell blades as well. There was an old Bell OSN on the hop/bounce matter and as I recall one Canadian accident that was attributed to that issue. The tail wag is usually due to a blade alignment or trunnion centering issue. Now whether the VH blades somehow facilitate entering those two conditions, I'll defer to your expertise.