Boeing 737-300 and Airbus Industrie 320-200 incident near Chicago, Illinois, March 23, 2006
On March 23, 2006 at about 3:07 pm local time, 2 aircraft, Boeing 737-300 (N309UA) and Airbus Industrie 320-200 (N493UA), were involved in the same incident near Chicago, Illinois. No one was hurt; 121 people were on board or involved. The weather was visual conditions (good weather).
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The NTSB's probable cause their words, unchanged
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.
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.
Source: NTSB aviation accident database, copy made October 4, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- March 23, 2006 · about 3:07 pm local time
- Place
- Chicago, Illinois · map
- Type
- Incident
- Injuries
- No one was hurt; 121 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft 1
- Boeing 737-300 · all 737-300s on the register
- Registration
- N309UA · registry record
- Damage
- Not recorded
- Flight
- Flight · scheduled airline rules (Part 121)
- Aircraft 2
- Airbus Industrie 320-200
- Registration
- N493UA · registry record
- Damage
- Not recorded
- Flight
- Flight · scheduled airline rules (Part 121)
The NTSB's narrative for the Boeing 737-300 final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The NTSB's narrative for the Airbus Industrie 320-200 final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record for the Boeing 737-300 from the NTSB's investigation tables, in plain English
Pilot
- Injury: no injuries
Co-pilot
- Injury: no injuries
The aircraft
- Landing gear: fixed
- Operator: United Air Lines INC
The flight
- Departed from: KORD Chicago IL
- Destination: KDCA Washington DC
- Flight plan: IFR
Weather at the time
- Wind: from 070° at 4 knots
- Visibility: 10 statute miles
- Sky: broken clouds at 2,600 ft
- Temperature: 39°F (4°C), dew point 27°F (-3°C)
- Altimeter: 30.25 inHg
- Observation at 8:56 am from KORD
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 5 | |||
| Passengers | 111 |
The factual record for the Airbus Industrie 320-200 from the NTSB's investigation tables, in plain English
Pilot
- Injury: no injuries
Co-pilot
- Injury: no injuries
The aircraft
- Landing gear: fixed
- Operator: United Air Lines INC
The flight
- Departed from: KORD Chicago IL
- Destination: KMCO Orlando FL
- Flight plan: IFR
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 2 | |||
| Passengers | 3 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
About this page
Everything above comes from the NTSB's public accident database: the narrative, probable cause and findings are the NTSB's own words, and the coded tables behind its report (pilot, aircraft, flight, weather, injuries, sequence of events) are written out in plain English. Pilots' ages, home towns and medical details are left out on purpose. The documents and photographs are the NTSB's docket, the folder of records gathered during the investigation, shown as the NTSB released them (the NTSB redacts some personal details first) and listed under the NTSB's own titles. This site's own text never names pilots, passengers or anyone else involved. A preliminary report describes what is known soon after the event and can change; the final report, with the probable cause, usually follows one to two years later and this page is refreshed when it does. Case number OPS06IA007.