Having spent some time with fount of all knowledge, Google, it seems to confirm my gut feeling that the inertial frame of reference relevant to the aircraft is the airmass it is moving through, not the ground. Indeed, the ground appears no more relevant than the centre of the solar system to the helicopter. If this is the case then being 'downwind' is also irrelevant in this context.
Load of examples such as the juggler here:
http://id.mind.net/~zona/mstm/physic...tialFrame.html
I realise this is at odds with Dennis's explanation and I hesitate to take a contrary point of view. NICK, where are you when we need you. Induced Drag is clearly thinking on the same lines as me.
I'd be happy to be proved wrong so as not to be at odds with Shawn, Dennis, FH1100, and just about everyone else but I can find no convincing physical reason to support the assertion that Ziggys accident was related his track relative to the wind direction other than ID's gradient explanation.
Come on guys, Ive got to be missing something here.
Edit: My interest is more than academic. I experienced a similar drop during an LPC a few years ago doing steep turns, fortunately at 1500ft. Lost a couple of hundred ft in a few seconds.