Sequence of Events
After a routine radio ramp check, Flight 629 taxied to runway 08R and at 1844 was in runup position, where it received ATC clearance for the flight to Portland, the first intended landing. The clearance required compulsory radio reports upon passing the Denver Omni and when climbing through 18,000 feet to its assigned altitude of 21,000 feet. Following takeoff, the flight reported its off time to the company as 1852 and reported passing the Denver Omni at 1856; this was the last communication from the flight.
At about 1903, Denver tower controllers observed two white lights, one brighter than the other, appear in the sky north-northwest of the airport and fall to the ground. Both lights were observed for 30–45 seconds and appeared to fall at approximately the same speed. There was then a momentary flash originating at or near the ground, which illuminated the base of the clouds, approximately 10,000 feet above. Controllers initiated action to determine if any aircraft were in distress. Radio calls were made to all aircraft in the Denver area of responsibility, and all except Flight 629 were accounted for. It was soon learned that the flight had crashed and all 44 occupants had been killed.
Investigation Findings
The disintegration of the aircraft in the air was caused by a bomb. The official probable cause, as determined by the Board, was the disintegrating force of a dynamite bomb explosion that occurred in the number 4 baggage compartment. The following findings were reported:
- At 1903, eleven minutes after departure, an in-flight disintegrating explosion occurred aboard Flight 629.
- The aircraft was climbing normally and was on course when the explosion occurred.
- Physical evidence showed conclusively that the explosion took place in the number 4 baggage compartment.
- The violence of the explosion and physical evidence proved that the explosion was not caused by any system or component of the aircraft.
- Physical evidence at the scene and laboratory tests confirmed that the explosive material was dynamite, in the form of a bomb.
- No evidence was found to indicate malfunction or failure of the aircraft or its components prior to the explosion.
Perpetrator
Two weeks later, on November 15, investigators confirmed that an explosive device had been placed on board by John Gilbert Graham, aged 23, who signed a US$37,500 life-insurance policy for his mother, who was on board. Convicted of murder and terrorism, he was sentenced to death and executed on January 11, 1956.