Narrative:

Shortly after assuming the local 1 position I had a few departures with multiple arrivals to runway 19R. Adw [arrival departure window] was in effect and everything was going as usual when I initiated aircraft X to line up and wait. I was waiting to shoot a gap between aircraft Y who was in the adw window and another aircraft who was approximately 5 miles out. Once the adw window was clear I gave aircraft X a takeoff clearance. Aircraft X began take off roll. As I normally do; I turned to look towards the approach end of 19R to ensure the aircraft wasn't going around. In my scan I spotted the aircraft passing the threshold and about to touch down. That is when I realized the size of the aircraft and noticed it was a B757. I immediately turned back towards the approach end of runway 25R to see what degree of commitment aircraft X was in their departure roll. My initial reaction was to cancel their take off clearance but aircraft X appeared to be at a high speed roll past taxiway A2. I assessed the situation and given the size of the aircraft; the outside air temperature and the speed aircraft X was at; I felt that it was in the best interest of the operation to allow aircraft X to rotate and continue. I watched to ensure that aircraft Y successfully landed and that no other intervention had to take place. I personally think B757 should be taken out of the adw order. However; given that it is currently a rule to ensure a B757 is wheels down before launching; I think briefing the rest of the facility or making this an unusual situations simulator would be great training. We don't often see a B757 using a [north-number] call sign. And for the few times that we do; we aren't necessarily applying adw. I believe it is easy to have a biased expectation that a [north-number] is associated with a larger or smaller aircraft.

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Original NASA ASRS Text

Title: Las Vegas Tower Controller reported not applying Arrival Departure Window procedures correctly leading to a loss of separation.

Narrative: Shortly after assuming the Local 1 position I had a few departures with multiple arrivals to RWY 19R. ADW [Arrival Departure Window] was in effect and everything was going as usual when I initiated Aircraft X to line up and wait. I was waiting to shoot a gap between Aircraft Y who was in the ADW window and another aircraft who was approximately 5 miles out. Once the ADW window was clear I gave Aircraft X a takeoff clearance. Aircraft X began take off roll. As I normally do; I turned to look towards the approach end of 19R to ensure the aircraft wasn't going around. In my scan I spotted the aircraft passing the threshold and about to touch down. That is when I realized the size of the aircraft and noticed it was a B757. I immediately turned back towards the approach end of runway 25R to see what degree of commitment Aircraft X was in their departure roll. My initial reaction was to cancel their take off clearance but Aircraft X appeared to be at a high speed roll past taxiway A2. I assessed the situation and given the size of the aircraft; the outside air temperature and the speed Aircraft X was at; I felt that it was in the best interest of the operation to allow Aircraft X to rotate and continue. I watched to ensure that Aircraft Y successfully landed and that no other intervention had to take place. I personally think B757 should be taken out of the ADW order. However; given that it is currently a rule to ensure a B757 is wheels down before launching; I think briefing the rest of the facility or making this an unusual situations simulator would be great training. We don't often see a B757 using a [N-number] call sign. And for the few times that we do; we aren't necessarily applying ADW. I believe it is easy to have a biased expectation that a [N-number] is associated with a larger or smaller aircraft.

Data retrieved from NASA's ASRS site 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.