Date: 202010
Local time of day: 1801-2400
Location: ZZZ.TRACON, US
Aircraft: Small Transport; Low Wing; 2 Turbojet Eng
Operator: Fractional
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class D ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Government
Reporter function: Supervisor / CIC
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Confusion; Situational Awareness
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Procedure; Human Factors; Environment - Non Weather Related; Staffing
Primary problem: Staffing

Narrative: We are concluding our last week of COVID scheduling. Normal operations during this reduced staffing period involve two open sectors: Combined Sector Name X (aka; The West Side with Sector 1 and Sector 2) and [other combined Sector Y] (aka; The East Side with Sector 3 and Sector 4). The West Side is generally a little busier because it handles most airport approaches save ZZZ1. The East Side is mostly departures. Splitting up the West Side in order to diffuse traffic would require opening both [Sector 1 and Sector 2] because the '[Combined Sector name] only' traffic isn't very busy. This would require a minimum of 4 CPCs and I only have five to cover the shift. Complexity picked up when 'Controller A' was working; so I went to an unused scope to help assist where needed (make/take hand offs; update data blocks; highlight untracked VFR targets; etc.) During this time of day; the airport was reporting haze and between 4 and 5 miles of visibility. The ILS is out at ZZZ2 and we use the VOR-B which under ideal circumstances works similar to the ILS but aircraft can hang the altitude up higher all the way to the VOR. This is unusual but not unheard of in VFR situations. In fact; to my recollection; all aircraft had executed the VOR-B in a 'straight in' manner which produces a sharper rate of descent. The traffic started to subside and Controller A was being relieved by Controller B. I returned to the Supervisor Desk to attend to some things there. When the controller on [Sector Y] got relieved; he alerted me to the fact that there may have been a separation error over ZZZ2 involving Aircraft X; ZZZ2 arrival on the VOR B and Aircraft Y on the ILS to ZZZ3. When I reviewed the replay; there indeed was a LoSS [Lack of Standard Separation]. Aircraft X remained at 026 until the VOR and then circled to right traffic to land; conflicting with Aircraft Y before divergence. Controller A's expectation had led him not to employ positive separation nor highlight the potential conflict to Controller B in the relief briefing. Further; Controller B never caught the development of the conflict nor issued a Traffic Alert after notified (late) by ZZZ2 Tower as to Aircraft X's intentions. I discussed this with both controller. Also; Controller A has been dealing with personal family issues. He had been given the opportunity to take as much time away from work as he needed; but indicated he wanted to work. He had not shown any outward signs of fatigue or stress in his work; but it should probably be noted.There are no set procedures or training in how to account for this because of the dynamics of the traffic load and who has responsibility to 'stagger' approaches in a manner to ensure separation. For example; a general rule of thumb might be that the [Sector 2] controller will stagger ZZZ2 arrivals for the Sector 1 controller; because the controller has more airspace to work with. But what if the majority of traffic is ZZZ2 arrivals? What if both airports have heavy inbounds? The problem is alleviated greatly when the ILS is put back in service; but when the area if experiencing IFR conditions; a 'go-around' produces the same problem. Because of the airport s' proximity to one another; the mountains to the east and the ZZZ4 BRAVO to the south; there aren't other approach options available.  Adding an emphasis for these scenarios in classroom training should probably be incorporated as a 'trap' to watch for; and mitigation strategies to account for it. This is a known issue; but a long term workable solution has been problematic and always seems to fall back on the controller fighting expectation bias and ensuring standard separation in a complex scenario. Perhaps a long range proximity alert system that helped a controller highlight these potential conflicts specific to this dynamic would help remind controllers that this needs careful monitoring at a minimum; advanced planning and positive separation at a maximum.




Synopsis: TRACON Front Line Manager reported a loss of separation and cited traffic complexity and staffing as contributing factors.