ASN Aircraft accident Douglas DC-6B N37559 Longmont, CO
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Status:Accident investigation report completed and information captured
Date:Tuesday 1 November 1955
Type:Silhouette image of generic DC6 model; specific model in this crash may look slightly different
Douglas DC-6B
Operator:United Airlines
Registration: N37559
MSN: 43538/224
First flight: 1952
Total airframe hrs:11949
Engines: 4 Pratt & Whitney R-2800-CB16
Crew:Fatalities: 5 / Occupants: 5
Passengers:Fatalities: 39 / Occupants: 39
Total:Fatalities: 44 / Occupants: 44
Aircraft damage: Destroyed
Aircraft fate: Written off (damaged beyond repair)
Location:Longmont, CO (   United States of America)
Phase: En route (ENR)
Nature:Domestic Scheduled Passenger
Departure airport:Denver-Stapleton International Airport, CO (DEN/KDEN), United States of America
Destination airport:Portland International Airport, OR (PDX/KPDX), United States of America
United Air Lines Flight 629 was a scheduled daily flight between New York-LaGuardia Field, New York, and Seattle, Washington. There were scheduled stops at Chicago, Illinois; Denver, Colorado; and Portland, Oregon, with crew changes at Chicago and Denver.
On November 1, 1955, this flight was routine to Denver where the flight landed at 18:11, 11 minutes late because of several brief ground delays. At Denver the aircraft was refueled to 3,400 gallons of fuel and was checked for the continued flight.
When the flight arrived at Denver, the rear cargo hold (No. 4), was emptied and thereafter loaded with mail, freight, and passenger luggage, all of which originated at Denver.
Flight 629 taxied to runway 8R and at 18:44 the flight was in runup position where it was given ATC clearance for the flight to Portland. Following takeoff the flight reported its "off time" to the company as 18:52 and thereafter reported passing the Denver VOR at 18:56. This communication was the last from the flight.
About 19:03 the Denver tower controllers saw two white lights, one brighter than the other, appear in the sky north-northwest of the airport and fall to the ground. It was soon determined that flight 629 had crashed.
Investigators determined that the tail section of the aircraft separated in mid-air following a violent explosion in the rear. The remaining aircraft then broke up.

On November 14, 1955, agents of the Federal Bureau of Investigation (FBI) took into custody John G. Graham, the son of one of the passengers. Thereafter, he was indicted for acts leading to the destruction of the aircraft by means of a bomb explosion.
Graham, who held a grudge against his mother as the result of an unhappy childhood, was the beneficiary of both her life insurance policies and her will. He wrapped dynamite sticks as a Christmas present.

Probable Cause:

PROBABLE CAUSE: "The disintegrating force of a dynamite bomb explosion which occurred in the no. 4 baggage compartment."

Accident investigation:

Investigating agency: CAB
Status: Investigation completed
Accident number: final report
Download report: Final report

Loss of control

» ICAO Accident Digest Circular 50-AN/45 (201-203)


photo of Douglas-DC-6B-N37559
accident date: 01-11-1955
type: Douglas DC-6B
registration: N37559
photo of Douglas-DC-6B-N37559
accident date: 01-11-1955
type: Douglas DC-6B
registration: N37559

This map shows the airport of departure and the intended destination of the flight. The line between the airports does not display the exact flight path.
Distance from Denver-Stapleton International Airport, CO to Portland International Airport, OR as the crow flies is 1570 km (981 miles).
Accident location: Approximate; accuracy within a few kilometers.

This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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Douglas DC-6

  • 704 built
  • 26th loss
  • 20th fatal accident
  • 8th worst accident (at the time)
  • 21st worst accident (currently)
» safety profile

 United States of America
  • 13th worst accident (at the time)
  • 70th worst accident (currently)
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