After seeing these pictures, I’ll throw out my theory of what happened, as I think it would best explain, considering the construction of the tail rotor system, how both blades could depart the aircraft simultaneously.
The s-76 tail rotor appears to be a smaller version of the UH-60, which uses an inboard and outboard retention plate to hold (and drive) the tail rotor paddles. There is an amount of clamping force that is checked with shims when installing the paddles and torquing the plates together, but that clamping force alone wouldn’t be sufficient to contain the blades from departing the aircraft.
As you can see from the schematic, the (graphite? Fiberglass? I forget) paddle spar has a hole in it that contains an oval shaped aluminum plug, with a hole in it for the pitch change shaft to go through, bonded into the spar(conveniently called a spar plug). The inner paddle is slid over the pitch change shaft and set into a recess in the inboard retention plate, then the outer paddle is placed over the inner one and recesses into the outboard retention plate.
I suspect the paddle failed at the spar plug area, as the spar is thinnest at the point either side of the plug. As the clamping force alone isn’t sufficient to contain the paddles, the now separated spar with blades attached overcame the clamping force and simply “slid” out from between the retention plate because of the massive rotational force. Pitch links probably didn’t even slow them down.
The only thing that makes me somewhat puzzled and could throw a wrench in my theory is the rubber boots shown still attached. On UH-60 these boots are bonded with Proseal to a piece of composite material that is in turn bonded to the spar at the inboard(retention plate side).
These are not structural parts of the paddle, just something to seal up the end of the blade root area to keep water
and debris out. I have seen these become disbonded from the spar before and they tend to tend to try to slide outboard towards the blade tip but they can only go a couple of inches.
The other end(blade side) is secured with a zip tie. So if the spar failed like I described the boots should have departed with the severed halves, unless the S-76 has a different attachment method?
I’d LOVE to watch the tear down of this assembly!🤣 As usual, Guess we will all have to wait for the investigation to see what really happened. ☹️
FltMech