Do you think if the crew noticed aircraft performance deterioration(ie ice)they may have talked to ATC.Having had the crap scared out of me many moons ago in a turboprop Otaki-Ferry,yes ice build up can be sudden but not that quickly an experienced crew would not recognise it.Especially as it was forecast and the boys had flown the route for years.
What was the last radar trace rate of descent?(Maybe the largest peice of airframe)
THERE WERE NO ATC COMMS!