UA 629 – Longmont Sabotage Bombing
Date of Incident: November 1, 1955
Location: Longmont, Colorado, USA
🧭 What Happened
United Airlines Flight 629, a Douglas DC-6B named “Mainliner Denver,” exploded mid-air 11 minutes after departing Denver Stapleton Airport. All 44 onboard were killed. Investigators determined the cause was a dynamite bomb placed in a passenger’s checked luggage — the first confirmed act of sabotage against a commercial airliner in the United States.
✈️ Aircraft Details
Flight Number: UA629 / UNITED 629
Aircraft Type: Douglas DC-6B
Registration: N37559
Route: LaGuardia → Chicago Midway → Denver Stapleton → Portland → Seattle
Fatalities: 44 (39 passengers, 5 crew)
Survivors: 0
🔍 Key Factors
- Explosion originated in rear baggage compartment (#4)
- 25 sticks of dynamite with a homemade timer
- Bomb placed in suitcase of passenger Daisie King
- Perpetrator: her son, John Gilbert Graham
- Motive: insurance fraud and personal revenge
📆 Timeline of Events
- 00:11 UTC – Arrival at Denver Stapleton
- 00:52 UTC – Departure from Denver
- 00:56 UTC – Last radio transmission
- 01:03 UTC – Mid-air explosion over Longmont
- 01:04 UTC – Debris falls across 6 sq mi of farmland
🎙️ Cockpit Voice & Flight Data
No CVR or FDR existed in 1955. Investigators relied on wreckage analysis, eyewitness accounts, and forensic testing. The explosion was so violent that the tail section separated instantly, and the aircraft broke apart before impact.
⚙️ Aircraft Systems & Failures
- Explosion destroyed empennage and control surfaces
- Fuel tanks ignited on impact
- Debris embedded up to 1 ft into soil
- Blast pattern confirmed internal sabotage
🛡️ Aftermath and Reforms
- John Graham arrested and confessed on Nov 13, 1955
- Convicted of murdering his mother; executed Jan 11, 1957
- First televised trial in Colorado history
- Prompted early calls for baggage screening and insurance reform
- Memorial efforts underway in Weld County