Nick you are correct, I use the wipers as a guide and if they are collecting ice I am planning altitude or heading changes to exit the area.
My experience with ice is only operational and from what I've seen it usually starts at the blade root and travels out.I've read somewhere, though I can't recall where that at 375 knots the temperature rise is appx 16 degrees. That would explain why it starts at the root.
From an operational point of view if you're in cloud below 0 degrees C, you're going to be picking up some ice.
In the good old days we use to transit icing areas but know flight in visible moisture below 0 degrees C is VERBOTEN and flying is much easier.
[ 04 November 2001: Message edited by: tech ]