B737 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Confusion; Situational Awareness
ATC Issue All Types; Conflict Ground Conflict; Less Severe
General None Reported / Taken
Human Factors; Procedure
I had a loss of separation because of the misapplication of visual separation. New procedure in place at LAS is called ADW (Arrival and Departure Window). Right before I was to take the Local 1 position I had a discussion with my supervisor regarding the potential for an aircraft to roll through the intersection while I was departing; fully complying with ADW; thus having two aircraft; both an arrival and departure on the same runway. He expressed to me he was under the impression it would be a negative situation; I believe he said runway incursion but I am not positive; but he indicated it was not legal to have two aircraft on the same runway in that situation we were discussing. Wouldn't you know later while working Local 1 applying ADW procedures (complying with all aspects to the best of my knowledge) an aircraft rolled to the end of 19R with traffic departing 25R. ASDE-X warnings screamed about converging traffic. I was very shook up and asked my assist to relieve me as my voice was shaking audibly on frequency. At the time of this incident I had traffic an A320 airborne and a B737 rolling. Before I cleared the B737 for takeoff with out delay I asked pilot to report previous departure in sight. He read back 'cleared for takeoff no delay maintaining visual separation with previous aircraft'. In between these two departures [I was] appropriately applying procedures per our 'rules;' I ended up with a departure and arrival on the same runway and ASDE-X screaming about converging traffic. Trying to keep my composure as I requested relief; I shipped the B737 to Departure without reiterating 'approved' or 'maintain visual separation'. Decide what your rules are before implementing a new procedure. Brief your employees properly; starting from the 'top down'. I feel the alarm from the ASDE -X; coupled with the conversation with my Supervisor led me to not close the loop. I was concerned I had done something wrong in applying our ADW procedures. I will also re-evaluate the phraseology and timing of when I request/approve visual separation.
LAS Controller experienced an ASDE-X event when Runway 25R landing traffic and rolling across Runway 19R activated the alarm due to departure traffic from Runway 19R; the less than clear ADW procedures were listed as contributory.