Date: 201502
Local time of day: 0001-0600
Location: ORD.Airport, IL
Aircraft: Medium Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ORD
Second aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Other / Unknown
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness
Second reporter function: Local
Anomaly: Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Automation Air Traffic Control
When detected: Taxi
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: I heard the aural alarm go off on the Airport Service Detection Equipment (ASDE)-X for 28R; looked up and saw Aircraft X on 28R at taxiway F while Aircraft Y on departure roll.I was not directly involved with the incident; I only witnessed it.


Second narrative: I was working North Local Control (NLC) landing runway 27L during the event. My workload was low; but the workload of the other controllers was much greater. As I was working my position; the Airport Service Detection Equipment (ASDE) alerted 'Warning..........runway 28R occupied.' After I heard warning; I quickly scanned my runway and then scanned the ASDE before the runway 28R occupied came through the speaker. As the location was apparent I noticed the blinking circles on the ASDE on 28R.  I then thought to myself 'It must be a false target;' but I did notice that a tagged aircraft and symbol for an aircraft was crossing runway 28R at taxiway Foxtrot. We routinely receive false/nuisance alerts usually involving runway 32L and taxiiing aircraft or false targets.  After realizing I didnt have any conflicts I spun around to look out the window.  It was then that I saw a Aircraft Y pointing northeast on the runway as an aircraft was departing (Aircraft X). As I noticed this Aircraft X passed Aircraft Y on the runway.  There was very little time between the alert and seeing the aircraft pass each other. It also appeared that there was very little distance between the two aircraft and I was very shook up as I have no idea how they avoided each other.I have never in my XX years of ATC been that terrified. I was not involved with either of the aircraft on my frequency. I just witnessed the runway incursion. I will say that there was little to say or offer for assistance as the event happened so fast and at the point we all realized what was happeneing; the time just wasnt there. The distance between EE and F on runway 28R is approx 1;900 feet. ASDE alerted in between N4/N5 and the departure aircraft seemed to be going very fast when I saw it out the window.At this point I'm not sure how the aircraft got on the runway. I was not directly involved with either aircraft. There are a few things that need to be highlighted in this event. 1) The constant false/nuisance alerts on runway 32L invlovling taxiing aircraft can lead to complacency with the alerts. 2) The ASDE leads not with where the aircraft are but 'Warning.'  Valuable time is spent letting us know a situation exists but wastes time we could use to avert a situtaion if it led with the location; especially when you have more than one runway in your jurisdiction.


Synopsis: ORD Tower controllers report of a runway incursion they observed.