What happened
The flight was operated under night cargo rules in known icing conditions. Before departure, a line serviceman observed ice accumulation on the aircraft's wings and recommended its removal. The pilot declined this suggestion. Approximately 45 minutes after takeoff, the pilot contacted air traffic control to report that a de-icing boot had failed. He described the boot as moving back and forth uncontrollably and stated he was struggling to maintain control of the aircraft.
The pilot reported needing full right aileron input to keep the wings level. He also noted a continuous loss of altitude and indicated that even with full rudder input, he could not stop the aircraft from turning to the left. The aircraft subsequently crashed into descending terrain while in a slightly nose-down attitude with the left wing low. The impact and subsequent fire destroyed much of the airframe, including a significant portion of the left wing. Propeller slash marks indicated that the engines were still providing power at the time of impact.
The investigation
Maintenance records showed no evidence of replacement, repair, or modification of the de-icing boots in the ten years prior to the accident. The pilot's wife indicated that he had previously been pressured to fly aircraft with known discrepancies. Weather advisories, specifically SIGMETs Golf 3 and 4, had warned of occasional severe mixed icing in clouds and precipitation.
Findings
The failure of the de-icing system in known icing conditions contributed to the loss of control. The pilot's decision to proceed despite visible ice on the wings and prior warnings about the aircraft's condition played a role in the outcome.