What is worrying however is that collegues are flying in the crowded skies of western Europe and don't realize that something is wrong when the radio is quiet for some time
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Not all that unusual I'm afraid to say. Although in all fairness it doesn't usually last as long as in this particular case.
We've been told that there is a known technical reason for this (with some radios). Nevertheless, I'm also inclined to reflect on just how much silence a cockpit crew would expect in a busy area of Europe in the middle of a very busy day without being aware that perhaps something's amiss? I've had the experience many a time in the middle of the night when traffic is very light, and there's been a protracted silence, that an aircraft has enquired if we're still there! I think this guy stayed quiet roughly for 55 mins or so.