The problem with Pprune is there are so many people here that if you say white is white, some smart Alec will prove that in certain circumstances, white is, actually, black, don't you know? We now get Airbus advice, and me told to do my homework, when such advice does not appear in the Boeing handbook. We are given unproven evidence from 2 crashes where icing may have been a factor, but it is unproven, and anybody quoting that as support for a wider definition is skating on thin ice! If you pardon the expression.
The OP asked a simple question which has been overcomplicated by numerous 'experts' here, quoting a totally different type. A little research about the OP would reveal he is evidently learning from a Boeing POV, not Airbus, and that was where my answer was based. There is no need to needlessly complicate for a foreign speaking poster- he was asking from an inexperienced learner working from a Boeing perspective, not Airbus, and that was the perspective my answer. So thanks for the lesson, but not needed, or desired, in this thread.
Now how does Antonov and Ilyushin play it then? Any advance on Tristars and Embraer? It's getting frightening to answer any queries here because there are always pedants who will prove your answer wrong for a type that is not even being asked about.