I suppose I can answer my own question --> As they pulled up the cut up slab sections, they disturbed the column, which was integrated with that last piece of slab which extended beneath, or stuck to the column. The column likely fractured in quick order, then slowly progressed as the...
It looks to me that the column base was destabilized by removing the slab. I'm not sure what precautions should have been taken to avoid that. I don't see the footing either.
Plenty? Oh, I missed that one.
Is it possible that by removing the slab at the base of the column, the effective six inch (or so) increase in column height tipped it over the edge? Answer: no, they couldn't cut right up against the column ... although on the thin side that cleaved off it...
So if the containment rebar is missing from that column, where else is it missing? What were they working on/with above the column to completely obliterate it. This story is much bigger than we know.
If it wasn't so serious I would laugh at the structural/facia brick differential and the idea that the facia layer can be removed with impunity. I'm not saying that was the case here but by extension, uniformed removal of any course of multi-wythed brickwork is inane.
The thin wall theory plays nicely into the out of phase oscillation theory (with the west adjoining bridge structue). A thin wall offers less resistance to lateral forces and can bow or fatigue easier, or rebar pullout can leave a much smaller percentage remaining to support the vertical load...
A hard landing can cause a boom strike as can a narrow set of in flight conditions, none of which make it a go to theory as an initiator for this incident. I don't need to wait for a certified gov report before I start to familiarize myself with publically available information and I hope...
The yaw isn't so much a loss of tail rotor function, it's that when the drive train seizes, the inertia of the lifting blades instantly spins the aircraft in the opposite direction with sufficient force that the tail rotor can't counter even if it were still functional.
My animated gifs are here (long) and here (short slo-mo) They are an interesting study in video editing. The source video is not continuous. The file size is controlled by algorithms leaving out "redundant" frames and substituting duplicates (or many more) of other frames to make up the lost...
The tail rotor shaft sits atop the tail structure, enclosed in its own shroud. The two inner members I believe are vertical and horizontal stabilizer linkages. I think they were just pinched as the tail snapped off.
I don't see any torsional component to the tail failure. It looks like a clean break to the right and slightly down, given the break line along the row of rivets. I don't know if a driveline seizure could whip the aircraft around so fast that the tail couldn't follow but that's what it seems...
