Incident Summary
A pilot conducted a night cargo operation in known icing conditions after receiving a weather briefing. Before departure, a line serviceman observed ice on the aircraft's wings and recommended its removal, but the pilot declined. Approximately 45 minutes after takeoff, the pilot reported to the Air Route Traffic Control Center (ARTCC) that a de-ice boot had 'blown' and he was experiencing control difficulties. He stated that the boot was 'going back and forth' and that full right aileron was required to maintain level wings. He also reported a continuous loss of altitude and noted that full right aileron could not prevent the aircraft from turning left. The aircraft subsequently crashed on descending terrain in a slightly nose-down, left-wing-low attitude.
Aircraft Damage and Conditions
Much of the aircraft, including a large portion of the left wing, was demolished by impact and post-crash fire. Propeller slash marks indicated that the engines were producing power at the time of impact. The accident occurred during dark night conditions, with low ceiling and fog present in a mountainous/hilly terrain area.
Maintenance and Pressure
Maintenance records showed no evidence of replacement, repair, or modification of the de-ice boots in the preceding 10 years. The pilot's wife revealed that he had previously been pressured to operate aircraft with known discrepancies. The flight encountered conditions warned by SIGMETs Golf 3 and 4, which indicated occasional severe mixed icing in clouds and precipitation.
Occupant Fate
Both occupants of the aircraft were killed in the accident.
Official Probable Cause Findings
The official probable cause findings from the investigation include: wing ice, total failure of the anti-ice/deice system (wing), inadequate maintenance inspection, failure to remove ice from the aircraft by the pilot in command, flight into known adverse weather conditions, company-induced pressure on the pilot, and the prevailing icing conditions.