Date: 202008
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: Small Aircraft; Low Wing; 1 Eng; Retractable Gear
Reporter organization: Government
Reporter function: Departure; Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Troubleshooting; Time Pressure; Situational Awareness; Distraction; Confusion; Communication Breakdown; Workload
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors; Environment - Non Weather Related; Procedure
Primary problem: Human Factors

Narrative: I think we're all familiar with the swiss cheese model/metaphor...this one has lots of swiss cheese. I had just got to work. I was taking the ZZZ position; which was combined with the ZZZ1 position. Is it normal for ZZZ1 to be combined with ZZZ at this time of the day you may ask?  Only during COVID. Should it have been split?  Should it be split more often than what it is? I don't know. I received the briefing from a Controller whose radar display settings are darker than mine (everyone's settings are darker/dimmer than mine). We're trying to maintain social distancing to the best extent possible so; basically; I'm not directly over her shoulder and I tried my best to see what everyone's doing as per the briefing. I can't remember the exact wording the Controller used; but it was something along the lines of Aircraft Y was descending via except maintaining 140. This is a standard practice right now because there's a TFR along the route of the ZZZZZ arrival.  What's not standard practice is putting a Aircraft Y on a STAR that's designed for turbojet and turboprop aircraft only. So; another hole in the swiss cheese is an aircraft on a route that shouldn't have been on it.The Controller before me issued the descend via except maintain 140 clearance so I don't know for sure if there might have been a read-back issue. Supposedly; management reviewed it all and said; 'we're clean.' We had legal separation. I doubt that; but that's not why I'm submitting this report. So; when the previous Controller told me the Aircraft Y was descending via except maintaining 140; 'expectation bias' started kicking in...though I didn't see his altitude for myself...from where I was at while I was receiving the briefing. The Aircraft X on the ZZZZZ1 arrival was approaching the airspace but I took the handoff on that guy just after I assumed the position so the center didn't have to spin him. That's when I should have looked to make sure Aircraft Y was meeting his restrictions. I did not though. What I was doing was trying to sign into the STARS; and I was (regrettably) wondering why the Controller was doing some things that; let's just say I; wouldn't have done. If you need to know what it was just make the request and I'll explain; but either way; it took away my attention from the conflict that was brewing. 100% on me. That's on my personality (which isn't great). The other issue that was distracting me; which I have a problem with; is an issue I've reported before. ZZZ2 GCA; has this weird automation issue where; if an aircraft is typed in; landing in a ZZZ3 sector the handoff will bypass the ZZZ sector and go straight to the ZZZ4 sectors. I refuse to believe this is an unsolvable issue. I just don't buy it. I'm not sure if it's a money issue or someone's just being lazy or what the issue is. But it's been going on for years. What had happened was; ZZZ2 GCA gave a VFR aircraft flight following to ZZZ6. As it was typed into ZZZ5; the autoflash or whatever they got there; directed the hand off to the ZZZ5 sector. The guy working that sector was a bit overzealous as he is new (though it'll turn out to be an incredibly fortuitous trait here in a minute) and just takes radar on anything flashing at him. So there's now a VFR aircraft calling me that I have no idea about and he's talking at me like I should know who he is and he's telling me about how he wants to take pictures for his survey work. I finish signing into my settings. I issue a couple of frequency changes. This specifically frustrates me because I've reported this before. I call the ZZZ4 sector to see if he did take radar on the aircraft to see what was going on with the automation and he did. So; now that I know he wants to take pictures; I go to give him a new code so there's not a problem with a center generated code  and a guy flying around for 4 hours taking pictures messing up someone else's hand off. All the while the expectation bias is that the two descend vias are separated. Ithink something else of a mundane nature happened in the mean time but I can't recall what it was. I remember what it was now. The previous Controller had an aircraft on a 'flow' that was a little off. The aircraft was supposed to be over or south of the ZZZZZ2 intersection on a heading of 280. The previous Controller had him north on a heading of 290. I remember being frustrated that I felt obligated to call and appreq (because I was trained to never appreq anything unless you had to) the heading north of ZZZZZ2 since I wasn't meeting the appropriate criteria. Instead; I just turned him to a 280 heading and just hoped I didn't piss off the center nor did it cause them to have a loss of any type. Next thing I know; that same overzealous ZZZZ4 Controller (who now had radar on Aircraft Y) came over to me and asked if I was good with the Aircraft X and Aircraft Y. I looked over and they were both at 140 converging. The Aircraft Y had descended early. The Aircraft X hadn't checked in yet; he was probably waiting to. I immediately put a 3 mile J ring on Aircraft Y. The Aircraft X does descend on the STAR and; initially; I was hoping the Aircraft X would descend under Aircraft Y. After evaluating for about a second and a half that it wasn't happening (because Aircraft X was doing what he was supposed to do as per the arrival); I can't remember what I did first; but I believe I issued an unrestricted descent to Aircraft X. I probably should have issued a traffic alert and I regret doing that now.  I then issued a vector Aircraft Y to the right hoping to increase lateral separation. After seeing that vertical separation and lateral separation wasn't going to give me what I needed...I issued a climb to Aircraft Y. I honestly can't remember if I called traffic or not. I hope I did...to at least one of them...but I don't recall. From what I remember; Aircraft X entered the J ring which was around Aircraft Y prior to there being 1;000 feet of separation (of course the Aircraft Y never climbed). I issued a descend via clearance back to Aircraft X. I then issued a heading and altitude back to Aircraft Y.So; to sum it all up. Supposedly; there wasn't a loss but there could have been and much worse. This is because of [Controller] in the area who better get recognition for a save...even if after all the review I'm totally or even partially at fault. That guy saved; at the LEAST; a TCAS and a NMAC. I've reported this to my area rep; my facility rep; my FLM (who was on the swing because we didn't have an FLM on the day shift only CICs- which was the Controller I received incidentally...in case anyone thinks there might be a personality conflict between us...there isn't...and the OM's who were on the day shift...I don't know their names. There's a lot to learn from this scenario. I never liked this box. I have recommended so much but it falls on deaf ears. Look through all my reports. ZZZ should be two sectors...it's one....and it's combined with another sector 99% of the time since COVID. ZZZ2 GCA should have equipment that has seamless interphase with us...but they don't.




Synopsis: TRACON Controller working combined positions reported an airborne conflict that could have been worse; but was saved by another Controller.