Originally Posted by
tcasblue
Just confirm the ice forms on a 30 degree Celsius surface. I find that difficult to believe. 30 degrees F perhaps?
Yes, ~30 deg. C - ~85 deg F is the upper temp limit for ICI.
PBA is pretty much correct - the initial Ice Crystals melt, cooling the surface temperature due to the phase change, additional IC hit the liquid water further cooling it (and the surface) until it gets cold enough that it freezes again. Eventually either there is an rpm change (accel) that initiates a shed, or the accumulation sheds on its own. The accel related sheds are the ones that tend to be a problem, since most of the accumulation will shed all at once. The CF6-80C2 main problem was this accel shed - ice would accumulate during an idle descent, then there would be a level off accel resulting in a shed that was enough to flameout the engine.
Obviously it takes a high concentration of IC before this becomes a problem - as I noted earlier often described as sounding like heavy rain on the flight deck. As VinRouge notes, ICI usually occurs over highly convective weather (e.g. thunderstorms) - the convection pushes moisture laden air to high altitudes, where it's so cold all that moisture turns into Ice Crystals.