I didn't think I had anything to add until I saw the ZK-OBL entry (post #20). I flew as a pax on this aircraft from Queenstown to Milford Sound (thank God it was my wife's idea, or I'd have never heard the end of it), and we endured possibly the most severe turbulence I've ever encountered in my career (as Fantome so aptly puts it: denture dislodging turbulence). And then, despite the pilot's alleged choice of a smoother route home, we had an equally grueling tumble-dryer type flight back. I did wonder then about the fatigue life of the BN-2 then, so the possibilty of a structural failure in this case is eminently possible.
Very sad about the young lady involved.