Narrative:

Las ATCT was on configuration number 1. This configuration consists of: departing runway 25R; landing runway 25L; departing and landing runways 19R and 19L. At the time of the incident; I was working local assist 1. One of my duties is to provide the sequence and departure priority to the controller. Local assist 1 monitors the local 1 frequency. We have two different local controls that control each side of the airport complex. The runways at las intersect at the departure end in this configuration. To remain compliant with the 7110.65; we must make sure aircraft are through the intersection before aircraft can land or depart safely. Essentially; each local has to 'take turns' departing their aircraft through the intersection. The local assist 1 determines who will depart. On this day and the day prior the asde-X (ground radar) had been out of service and awaiting parts. Usually when the asde is in service; the local assist can look upon the asde and determine what each controller has without having to physically get up and walk to each side of the tower to look at the pending departures that each of the two controllers have. I had to get up and walk to the opposite end of the cab away from my position to see what local 2 had to depart while turning an extra set of eyes away from the local 1 operation. When I got back to sit down; I noticed air carrier X holding short runway 25R at alpha 5 and air carrier Y rotating and airborne just pass alpha 5 on runway 25R. It seemed innocent enough until air carrier X questioned the local 1 controller; 'I am I still cleared to cross?' the controller responds in the affirmative and air carrier X replied; 'okay.' but air carrier Y was rolling.' at this point I'm still confident that nothing went wrong until I asked the controller did air carrier X have a point. The controller was a bit rattled and that's when I realized he tried to cross runway 25R with air carrier X; but cleared air carrier Y right afterwards. Luckily; air carrier X was well aware of the going on's and he didn't move until air carrier Y was well passed and airborne. One of the most used tools at the larger; busy airports is the asde-X ground radar. The asde-X is not a substitute for the windows but we have come to rely on it as part of the routine scan. In this particular scenario; the asde-X being inoperable affected both the local 1 and local assist. I had to get up and turn my back to the operation whereas when the asde-X is in operation I can stay engaged and control from one spot. Even though I have local 1 frequency in my ear; I still could not equate what was going on without actually seeing and hearing the incident at the same time while it was unfolding. What good is an assist when I have to have my back turned.

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Original NASA ASRS Text

Title: LAS Controller described a near runway intersection conflict event prevented by pilot action/s after noting a departure aircraft rolling.

Narrative: LAS ATCT was on Configuration Number 1. This configuration consists of: departing Runway 25R; landing Runway 25L; departing and landing runways 19R and 19L. At the time of the incident; I was working Local Assist 1. One of my duties is to provide the sequence and departure priority to the Controller. Local Assist 1 monitors the Local 1 frequency. We have two different Local controls that control each side of the airport complex. The runways at LAS intersect at the departure end in this configuration. To remain compliant with the 7110.65; we must make sure aircraft are through the intersection before aircraft can land or depart safely. Essentially; each local has to 'take turns' departing their aircraft through the intersection. The Local Assist 1 determines who will depart. On this day and the day prior the ASDE-X (Ground RADAR) had been out of service and awaiting parts. Usually when the ASDE is in service; the Local Assist can look upon the ASDE and determine what each controller has without having to physically get up and walk to each side of the Tower to look at the pending departures that each of the two controllers have. I had to get up and walk to the opposite end of the cab away from my position to see what Local 2 had to depart while turning an extra set of eyes away from the Local 1 operation. When I got back to sit down; I noticed Air Carrier X holding short Runway 25R at Alpha 5 and Air Carrier Y rotating and airborne just pass Alpha 5 on Runway 25R. It seemed innocent enough until Air Carrier X questioned the Local 1 Controller; 'I am I still cleared to cross?' The Controller responds in the affirmative and Air Carrier X replied; 'Okay.' But Air Carrier Y was rolling.' At this point I'm still confident that nothing went wrong until I asked the controller did Air Carrier X have a point. The Controller was a bit rattled and that's when I realized he tried to cross Runway 25R with Air Carrier X; but cleared Air Carrier Y right afterwards. Luckily; Air Carrier X was well aware of the going on's and he didn't move until Air Carrier Y was well passed and airborne. One of the most used tools at the larger; busy airports is the ASDE-X Ground RADAR. The ASDE-X is not a substitute for the windows but we have come to rely on it as part of the routine scan. In this particular scenario; the ASDE-X being inoperable affected both the Local 1 and Local Assist. I had to get up and turn my back to the operation whereas when the ASDE-X is in operation I can stay engaged and control from one spot. Even though I have Local 1 frequency in my ear; I still could not equate what was going on without actually seeing and hearing the incident at the same time while it was unfolding. What good is an assist when I have to have my back turned.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.