Ed Winchester: that brings back memories, and yes that was the statement I was looking for (albeit -30 degrees!!). The mil fine tune it to some degree by putting a figure on it (1000m, probably because thats the dividing line between fog and mist?).
However I'm sure the mil also restrict snow to flying in those conditions 'below 500m' do they not?
You failed to mention also that precipitation is also included in the definition. In fact any precip in this range incurs some kind of airframe or engine icing actions. I would suggest that since rain/drizzle is precip, then so too is snow. Wet snow most certainly is.
CTD: My definition of visible moisture is rain / fog / cloud / snow / anything with water molecules in it. Provided you stay away from this then one can fly down to whatever the FLM tells you: -30 degrees for example. So flying around sub zero is a very common practice over here too!! but not in visible moisture, unless that particular model is specially fitted for sub zero flight envelopes (EC155, S76, puma, S61 for example).
[I know that below a very low temp (can't remember offhand I think it's -20 degrees?) one encounters supercooled droplets and yet lower than this: ice crystals, where a/c fly because they have negligible effect on the airframe, but that's not helo territory, I believe!]
Open to scrutiny??
------------------
Thermal runaway.
[This message has been edited by Thomas coupling (edited 09 March 2001).]