What happened
On the afternoon of the accident, Flight 21 was operating a scheduled domestic service originating in Vancouver, British Columbia, with planned stops in Prince George, Fort St. John, Fort Nelson, and Watson Lake, Yukon Territory. The aircraft departed under an instrument flight plan at 14:42 PST, following the Victor 300 and Blue 22 airways.
While traveling northbound on the Blue 22 airway near Hope, the crew established contact with CPA Flight 22. At 15:17, the pilot received authorization to deviate from the original track to fly directly toward Williams Lake, a route that would take the aircraft west of Ashcroft. By 15:29, the flight reported to Vancouver Air Traffic Control that it had passed Ashcroft at an altitude of 16,000 feet and provided an estimated arrival time for Williams Lake.
At 15:38, the Vancouver Centre attempted to contact the aircraft but received no response. Shortly thereafter, three distress calls were detected by air traffic controllers. During this period, witnesses near Gustafson Lake observed the four-engined aircraft flying through clear skies approximately 20 miles west of 100 Mile House. Observers reported hearing an explosion, after which smoke became visible and the tail section detached from the fuselage. The remaining wreckage entered a nose-down spiral to the left, eventually impacting a forested area roughly 4.5 miles north of Gustafson Lake at 15:41. The accident resulted in 52 fatalities.
Findings
The investigation determined that the destruction of the aircraft was caused by the explosion of a device, which led to the structural disintegration of the plane while in flight.