United Airlines Flight 629

United Airlines Flight 629

A United DC-6 at Stapleton Airport
Occurrence summary
Date	November 1, 1955
Summary	Bombing
Site	Longmont, Colorado 40°12′0.51″N 104°57′21.96″W / 40.2001417°N 104.9561000°W / 40.2001417; -104.9561000Coordinates: 40°12′0.51″N 104°57′21.96″W / 40.2001417°N 104.9561000°W / 40.2001417; -104.9561000
Passengers	39
Crew	5
Fatalities	44 (all)
Survivors	0
Aircraft type	Douglas DC-6B
Aircraft name	Mainliner Denver
Operator	United Airlines
Registration	N37559
Flight origin	LaGuardia Airport, New York, New York
1st stopover	Chicago Midway International Airport, Chicago, Illinois
2nd stopover	Stapleton International Airport, Denver, Colorado
3rd stopover	Portland International Airport, Portland, Oregon
Destination	Seattle-Tacoma International Airport, Seattle, Washington

United Airlines Flight 629, registration N37559, was a Douglas DC-6B aircraft also known as "Mainliner Denver", which was blown up with a dynamite bomb placed in the checked luggage on November 1, 1955. The explosion occurred over Longmont, Colorado at about 7:03 p.m. local time, while the airplane was en route from Denver, Colorado, to Portland, Oregon, and Seattle, Washington. All 39 passengers and five crew members on board were killed in the explosion and crash.

Investigators determined that Jack Gilbert Graham was responsible for bombing the airplane to kill his mother as revenge for his childhood and to obtain a large life insurance payout. Within 15 months of the explosion, Graham—who already had an extensive criminal record—was tried, convicted, and executed for the crime.

The flight had originated at New York City's La Guardia Airport and made a scheduled stop in Chicago before continuing to Denver's Stapleton Airfield and landed at 6:11 p.m., 11 minutes late. At Denver the aircraft was refueled with 3,400 US gallons (13,000 L) of fuel, and had a crew replacement. Captain Lee Hall (a World War II veteran) assumed command of the flight for the segments to Portland and Seattle.

The flight took off at 7:52 p.m. and at 7:56 p.m. made its last transmission stating it was passing the Denver omni. Seven minutes later, the Stapleton air traffic controllers saw two bright lights suddenly appear in the sky north-northwest of the airport. Both lights were observed for 30–45 seconds, and both fell to the ground at roughly the same speed. The controllers then saw a very bright flash originating at or near the ground, intense enough to illuminate the base of the clouds 10,000 feet (3,000 m) above the source of the flash. Upon observing the mysterious lights, the controllers quickly determined there were no aircraft in distress and contacted all aircraft flying in the area; all flights were quickly accounted for except for United Flight 629.