Originally Posted by
Capt Claret
10 degrees, but measured how?
On the Douglas/Boeing 717 it's 6 degrees, C, TAT. Even with an indicated TAT of up to 20C, I've seen quite large ice accumulation on th wiper arms & blades. A check of the OAT even at +20 TAT or more, can reveal sub zero temps.
I think the point is whether the situation leads to Ice stick to engine inlets or not. Ice accumulation on windows doesnt necessarily shows hazardous Icing condition.