Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7.5
Situational Awareness; Human-Machine Interface
ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Human Factors
I took over the Local Control (LC) position. Airport Operations (Ops) X plus 1 had just been put on the runway to repair lights. The RID [Runway Incursion Device] was activated. A few minutes later Ops moved farther down the runway and asked when the next arrival was. I looked at my strips and told him 20 plus minutes. He said that was plenty of time for him to finish up. I'm estimating maybe 10 minutes later; I noticed Aircraft X on a wide left downwind for ZZZ. I realized I did not have his strip for some reason and started looking for it in the recycle bin. I found it; and a few moments later Aircraft X checked on and I cleared him to land; I had completely forgotten about Ops on the runway.On about a 2.5 mile final; Aircraft X said he saw someone on the runway. I sent him around and Ops said they were exiting. I switched the Aircraft X to the crossing runway and he landed safely. I checked the RID and saw the volume was turned all the way down; I should have noticed that the first time I talked to Ops. I'm sure I scanned the runway but at this point; I don't know how I could have missed the vehicles. The sun was going down and the shades were still pulled down; we also have very large posts that can obstruct our view and we need to move to see around them sometimes. I'm not sure if any of that was a factor or not in forgetting about them. I do remember thinking that the Ops should be no factor for anyone when I thought the next arrival was proposed for more than 20 minutes out; I must have let my guard down. I usually write out a strip or a reminder of vehicles and put it in front of me or on top of my proposal strips but today for some reason I did not do that. This situation was completely my fault and I can't think of any recommendations for the position; just for myself. Even though there is no specific volume requirement; I plan on checking the RID and turning it up very loud when I activate it from now on. I do think it is a very useful tool; I use it often; and I have never forgotten about a vehicle before. I need to continue working on and improving my scan; write out a strip or a reminder of the Ops vehicle. I also think I will ask the Ops to advise when they are moving from light to light. If I had done that; I would have talked to the Ops vehicle a few more times and maybe would not have forgotten about them.
Local Controller reported forgetting about vehicles on a runway when the arrival aircraft alerted Controller to the fact there were vehicles on the runway.