NTSB Identification: OPS06IA007A
Incident occurred Thursday, March 23, 2006 in Chicago, IL
Probable Cause Approval Date: 11/30/2007
Aircraft: Boeing 737-300, registration:
Injuries: 121 Uninjured.

NTSB investigators used data provided by various sources and may have traveled in support of this investigation to prepare this aircraft incident report.

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 National Transportation Safety Board determines the probable cause(s) of this incident to be:

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.

Full narrative available

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