Narrative:

Aircraft X was direct sff airport expecting a visual approach; descending at pilot's discretion to 7000 ft. There were two tracks between aircraft X and sff in the 6400 ft MVA. I was monitoring them for possible conflict. I turned aircraft X shortly after to heading 250; descend and maintain 6000 ft. I told the pilot [it was a] vector for the visual approach; but it was also for traffic. I made a traffic call to aircraft X before turning them. I am really not sure why I descended aircraft X to 6000 ft at this point; and also why I did not catch the mistake. When I did realize the mistake; I scanned and turned aircraft X to a more direct heading (280) and was considering descending them to 6000 ft but then realized they were already level at 6000 ft. Since aircraft X was now leaving the 6400 ft MVA I did not see the point in issuing a low altitude alert at this time. My next transmission was to point sff airport out to them; they had it in sight; and I cleared them for the visual approach and switched communications to sff tower.this happened during a lull in traffic. Er (east radar) wr (west radar) had been split previously due to volume/complexity. They were combined to accomplish a team briefing. I agreed to combine it at the time. During the event; there was only myself and one other cpc (certified professional controller) in the room; working mr (missoula radar) combined with [another sector]. Even watching the falcon replay I am not sure what possessed me to descend aircraft X to 6000 ft; and why I did not catch the mistake until it had already happened. This is a MVA that I am familiar with and it was displayed on my position at the time. I did not ask for help; and I didn't feel it was needed at the time. In hindsight; another set of eyes might have prevented my mistake. Actually it may be the only thing that could have prevented it.

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Original NASA ASRS Text

Title: GEG TRACON Controller reported descending an aircraft below the MVA.

Narrative: Aircraft X was direct SFF airport expecting a visual approach; descending at pilot's discretion to 7000 ft. There were two tracks between Aircraft X and SFF in the 6400 ft MVA. I was monitoring them for possible conflict. I turned Aircraft X shortly after to Heading 250; descend and maintain 6000 ft. I told the pilot [it was a] vector for the visual approach; but it was also for traffic. I made a traffic call to Aircraft X before turning them. I am really not sure why I descended Aircraft X to 6000 ft at this point; and also why I did not catch the mistake. When I did realize the mistake; I scanned and turned Aircraft X to a more direct heading (280) and was considering descending them to 6000 ft but then realized they were already level at 6000 ft. Since Aircraft X was now leaving the 6400 ft MVA I did not see the point in issuing a low altitude alert at this time. My next transmission was to point SFF airport out to them; they had it in sight; and I cleared them for the visual approach and switched communications to SFF tower.This happened during a lull in traffic. ER (East Radar) WR (West Radar) had been split previously due to volume/complexity. They were combined to accomplish a team briefing. I agreed to combine it at the time. During the event; there was only myself and one other CPC (Certified Professional Controller) in the room; working MR (Missoula Radar) combined with [another sector]. Even watching the FALCON replay I am not sure what possessed me to descend Aircraft X to 6000 ft; and why I did not catch the mistake until it had already happened. This is a MVA that I am familiar with and it was displayed on my position at the time. I did not ask for help; and I didn't feel it was needed at the time. In hindsight; another set of eyes might have prevented my mistake. Actually it may be the only thing that could have prevented it.

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.