THE PILOT'S IMPROPER INFLIGHT DECISION TO CONTINUE FLIGHT INTO KNOWN ICING CONDITIONS. FACTORS WHICH CONTRIBUTED TO THE ACCIDENT WERE: THE PILOT'S FAILURE TO OBTAIN UPDATED WEATHER INFORMATION PRIOR TO DEPARTURE, THE ICING CONDITIONS, AND THE DEGRADED AIRCRAFT PERFORMANCE DUE TO AIRFRAME ICE AND THE PILOT'S FAILURE TO RETRACT THE LANDING GEAR.