What happened
During a flight traveling from Buckley AFB in Denver toward Seattle, the crew encountered difficulties maintaining their assigned cruising altitude of 12,000 feet. After the navigator notified air traffic control of these altitude maintenance issues, the aircraft was authorized to descend to 10,500 feet.
Shortly after this descent, the copilot reported encountering icing conditions and requested permission to climb back to a higher altitude. Approximately 20 minutes later, while flying at 10,000 feet amidst marginal weather, the four-engine aircraft impacted the side of Mt Tobin, which stands at an elevation of 2,980 meters. The wreckage was located by search teams several hours after the event, positioned roughly 300 meters below the mountain's summit. There were 19 fatalities and no survivors.
Findings
Investigations into the crash determined that the accident was not triggered by the reported icing conditions. Instead, the primary factor was a loss of control resulting from atmospheric downdrafts.