What kind of aerodynamic load would cause the tail to come off a helicopter? I see the S76 has some sort of stabilizer but it doesn't look big enough to apply that kind of load. Surely the rotor isn't capable of doing it. Do you think it hit something?
The main rotor actually is capable of doing it and from what I can see in the grainy video, the section of tail boom that is laying there separate from the rest of the debris is commensurate with a rotor strike. And again the video is grainy but if you look toward the opposite direction from where the tail is and where the smoke was wafting up, I believe what I saw there are (two) of the original (four) main rotor blades. Those items are laying more or less parallel (not of course normal since they are installed at 90 deg. to each other) and seem to be connected to a basically unidentifiable piece of (stuff) but which could well be the main transmission, which drives them. So my speculation would be that the main rotor hit and severed the tail section, either due to some sort of mechanical failure, or by a very violent series control inputs aimed at collision avoidance arising from the very poor visibility (fog) in the area and the rising slope of the surrounding terrain. They could also have actually got close enough to trees in the bad vis. to have had a main rotor strike, although that scenario doesn't quite fit the lay of the land vis a vis the direction of the debris field. It will take some time to pick up all those pieces and sort them but I would be looking right away for evidence of main rotor leading edge material on sections of that tail piece.