No hunch yet
gB, I am just trying to look at possibilities. I am not advocating any position yet. The fracture of the skin along the spar line makes me suspicious of one type of failure I have seen on an entirely different (F-111) aircraft, where an ineffective bond between a rudder mast and the core led to fatigue cracking of the skin and subsequent in-flight failure of the rudder.
Now almost every designer does not even consider this failure as possible, because the shear strength of core is an order of magnitude lower than the shear strength of the adhesive, so in many designs, this failure is not even analysed. In cases where the core-to-spar bond is ineffective (or fails) the out of plane shear loads must be carried by only the skins, and given that the R44 stainless steel skins are only about 0.006 inches thick, this failure mode is a possibility.
The photos of the rear of the spar will be of importance because if there is no adhesive on the spar (or minimal amounts of adhesive on the spar) then it is of fundamental importance to carefully check the skin failure using SEM or even just optical microscopy to see if there is any evidence of fatigue in the skin fracture. A further complication is that if they need SEM to find traces of adhesive, then there is another failure mode which can be significant and may lead to a different cause of failure.
If there is a significant amount of adhesive on the spar, then this failure mode is excluded.
If there is minimal or no adhesive and if there is evidence of fatigue in the skins then this approach must be further investigated. Again, I would expect that failure of the blade in this manner would result in blade impact on the fuselage as one blade looses lift, and apart from some indirect observations, I have not seen any evidence of such impact.
Another reason to consider this aspect is that it is unusual to have a segement of blade snapped off like that. If the segment was dislodged by impact, it must be out of plane to cause the skin to fracture at the back of the spar. The bond to the spar is only of the order of 0.5 inches long in the direction of rotation so impact with the water would be expected to cause peel failure of the skin-to-spar bond, rather than fracture of the skin.
These are my thoughts. I am NOT at this stage suggesting that this was the cause of the crash. All I am saying is that a simple investigation would exclude any further consideration of that factor.
Let's see what the photos look like. And in anticipation of the "leave it to the crash investigation experts" responses, I would bet the family jewels on the fact that adhesive bond failures constitute less than 2% of an average investigator's range of experiences, let alone expertise. This has been my bread and butter for forty years.
At 65 years old, the family jewels are not worth much these days.
Regards
Blakmax