Air Traffic Control Developmental
ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Procedure; Human Factors
When I had taken the GC [Ground Control] position; RWY 03/21 had just been returned to GC after a small arrival to the runway. RWY 03/21 is typically used by GC unless prior coordination usually when traffic permits a small prop to land on it and [Local Control] LC2 requests use of it from GC. LC2 had requested the use of RWY 03/21 for another arrival no more than 15 minutes after I took the position. I; working GC had also [Clearance Delivery] CD/FD combined with me; so I had multiple things taking my attention. I authorized the use of 03/21. Aircraft X had called for taxi and I gave them standard routing for the flow we were in; 'RWY 10L; taxi via Tango; Kilo; Cross RWY 21.' I had forgotten that I had given 03/21 to LC2 position. The other LC had come over and was standing next to me which I thought was strange and I made a comment to why he was there and he drew my attention the fact that Aircraft X was crossing the departure end of RWY03 and Aircraft Y was short final for that runway on the opposite end. The LC2 controller was made aware of the situation at the same time. We observed that Aircraft X had been clear of the runway edge before Aircraft Y crossed the landing threshold. In air traffic control; we can't always rely on our memories - there is too much at stake for that. That is why we have memory aids that we utilize. I was using a memory aid when this occurred and my scan had failed me. I had gotten into a flow that is more common and rattled off a standard instruction without giving a second thought to it. In order to prevent this situation from occurring again; I need to utilize my good scanning techniques that have saved situations from happening in the past. By doing this; I would have seen the memory aid and could have and will prevent this from happening in the future.
Portland Tower Ground Controller reported crossing an aircraft; while the Local Controller had an aircraft on final.