United Air Lines Boeing 737-300 incident
Boeing 737-300 and Airbus Industrie 320-200 · Incident: near collision between aircraft during takeoff
Event
- NTSB case
- OPS06IA007
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Incident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- Airline
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Aircraft 1 · Boeing 737-300
- Aircraft type
- Boeing 737
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N309UA
- Operator
- United Air Lines
- Onboard fatalities
- Unknown
- Route
- From Chicago O'Hare International Airport (KORD), Chicago, ILTo Ronald Reagan Washington National Airport (KDCA), Washington, DC
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 121: Air Carrier
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Takeoff · rejected takeoff
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Near collision between aircraft
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- None
Aircraft 2 · Airbus Industrie 320-200
- Aircraft type
- Airbus 320
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N493UA
- Operator
- United Air Lines
- Onboard fatalities
- Unknown
- Route
- From Chicago O'Hare International Airport (KORD), Chicago, ILTo Orlando International Airport (KMCO), Orlando, FL
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 121: Air Carrier
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Taxi · to runway
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Near collision between aircraft
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- None
Cause areas
- Control tower › Improper
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
On March 23, 2006, at 0907 Central Standard Time, a runway incursion occurred between United Airlines (UAL) flight 604, a Boeing 737-300, and UAL1520, an A-320, at Chicago O'Hare International Airport (ORD) during daylight visual meteorological conditions. The north local controller cleared UAL604 for takeoff from runway 4L while UAL1520 was crossing the runway. The UAL604 co-pilot looked out the window and saw the A320 moving at a fast rate toward the runway, aborted the takeoff, and advised the controller that they were aborting their takeoff for the crossing traffic. The co-pilot stated that they did not get above taxi speed during their departure. Separation was lost with closest proximity of approximately 600 feet, the distance from approach end of runway 4L to taxiway H. AMASS did not activate.
Probable cause
The probable cause of this incident was the ORD tower local controller's failure to provide sufficient separation between two aircraft departing intersecting runways. Contributing to the incident was the ORD local monitor's failure to monitor the situating and advise the local controller of the developing situation.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record OPS06IA007
- Event ID
- 20060411X00417
- Case number
- OPS06IA007
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status, damage. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: d375b24dc0a5257bd234fc309cf62ae02704b785f34fdd8a15f69525243fa291; retrieved 2026-09-18T14:54:22.460Z.