talkpedlar - based on the reported "bang"
Not hoping to speculate on this accident, but a general question - why would mast bumping lead to a loud "bang"? the tail looks intact (no obvious strike), if the mast had sheared would that itself be audible from the ground? or is it that without the weight of the helicopter keeping the mast vertical the remaining output from the MR gearbox would start to flail around ripping itself to bits, which in turn would surely dismount the gearbox, and drivetrain etc... just wondering from your history of accident investigation.
Cheers