The Airworthiness Concern Sheet shared by
TwinHueyMan in #428 doesn't mention the New York accident, rather a 206L, N9984K, that landed safely in Washington state on 26 Sept 2024 despite substantial damage to the tailboom following continued (vertical) vibrations, see:
https://asn.flightsafety.org/wikibase/454639. Still, is there a connection?
I have various comments on a few of the earlier posts:
Lonewolf_50 (#423): From the video you perceive a left yaw motion of the fuselage which you note would be contrary to a loss of tail rotor thrust. But several others perceive a right yaw of the fuselage which would then be consistent with a loss of tail rotor thrust. Watching the video it is hard to tell which direction the yaw actually is (see of example zoomed in clip from 16:39 onwards in the video linked at #391).
JamesT73J (#420): You ask wouldn't the VH hop ever be more than an "uncomfortable experience"? That isn't how some seem to describe it elsewhere on this thread and on the VH blades thread linked by Chock Puller at #361. It sounds scary in some cases.
hanche (#415): You mention an object seen briefly as the tail departs. If you look at the wreckage images in #363, it seems likely the rotors cut various parts of the tailboom so many smaller pieces were probably cut away. It would be very hard to work out which they are in the video, even the original version.
AAKEE (#414): Thanks for the image of your analysis of the audio from the break-up. The NTSB would surely be using that audio to try to help work out what occurred. When you refer to the "rotor assembly winding down" I assume you mean after it had already detached from the fuselage rather than earlier on? My post #340 has a screen shot that suggests one blade might be shorter than the other by that point but that could still be an illusion due to the pixelated image. Other screen shots I attempted didn't show such asymmetry in blade length. If that portion of the rotor departed in the air, it would still need to be determined whether that happened first or only after the rotor(s) struck the tail boom etc.
TwinHueyMan (#411): You feel there is a greater prospect of mast bending on ground impact than when the rotors detached from the helicopter(s). I can see either event could be violent enough to cause the damage that can be seen on the mast(s). To roughly compare one against the other, consider the kinetic energy stored in the rotor at cruise and the energy of a free falling rotor hitting the ground. I roughly estimate the 206L rotor might have 840 kJ of stored energy. If rotor strikes fuselage that can translate to a lot of force or moment exerted on the mast. If rotor is assumed to fall around 500ft (1437' msl - 900' msl) then pessimistically, and neglecting any autorotation or drag, it would hit the ground at around 57 m/s. Assuming the rotor system above the mast is around 140kg, then it collapsing onto the mask on impact would equate to around 230 kJ of energy release, so around 30% of the energy stored in the driven rotor when torn from the fuselage. I realise this is a crude comparison and the reality will all depend on how kinetic energy converts to damage to the components.
wrench1 (#410): You indicate fatigue cracks in blade spar of the Kentucky accident. But are you referring to the loss of the 206L-1 N114AE on 6 June 2013? The NTSB final report makes no reference to "fatigue" and I couldn't find fatigue mentioned in the airframe report of that accident either.