Background
The pilot received a weather briefing before starting a night cargo operation in known icing conditions. Prior to the flight, a line serviceman noticed ice on the aircraft's wings and suggested its removal, but the pilot declined. The pilot's wife later indicated that the pilot had previously been pressured to fly aircraft with discrepancies.
Flight Events
Approximately 45 minutes after takeoff, the pilot reported to air traffic control that a de-ice boot had 'blown' and that he was having difficulty controlling the aircraft. He stated that the boot was 'going back and forth' and that full right aileron was required to keep the wings level. Additionally, he reported a continuous loss of altitude and said that full right aileron would not keep the aircraft from turning to the left.
Crash and Investigation
The aircraft subsequently crashed on descending terrain while in a slightly nose-down, left-wing-low attitude. Much of the aircraft, including much of the left wing, was demolished by impact and fire. Propeller slash marks indicated that the engines were providing power at the time of impact.
Maintenance records contained no information regarding replacement, repair, or modification of the de-ice boots in the previous 10 years. SIGMETs Golf 3 and 4 had warned of occasional severe mixed icing in clouds and precipitation.