Date: 202009
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: Government
Reporter function: Approach; Departure
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Training / Qualification
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Conflict Airborne Conflict
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Environment - Non Weather Related; Human Factors
Primary problem: Human Factors

Narrative: This was day one of resuming training for both myself as instructor; and for the trainee; since the COVID-19 schedule began.  The radar positions were previously de-combined; but were combined up just before beginning training.  Shortly after; traffic and complexity increased rapidly.  As it was getting more difficult to complete a timely and accurate scan; Aircraft X was descending on a vector to the airport; and was on a converging course with an un-identified VFR tag at 7;500 feet indicated.  Before realizing this conflict; Aircraft X reported traffic up ahead.  The trainee issued traffic and a heading away; but not a traffic alert.  Aircraft X then informed us he was executing a TCAS RA; at which point we issued a traffic alert and to advise when complete.  He finished the RA; and continued on vectors to the airport.Traffic throughout the airspace has increased to a point in which multiple positions should have been used; both identified; controlled traffic; as well as VFR traffic saturating the airspace.  In addition to the traffic factors; the Supervisor position had just been switched over to a Controller; so the Controller in charge of the TRACON was fulfilling several duties at that time while the Supervisor was doing other duties.  This led to a lack of overall awareness throughout the TRACON; with more traffic at hand than controllers and supervision present. I recommend that supervisory personnel and controllers alike; myself included; be more vigilant of rapidly increasing traffic; and take action to de-combine positions in a more timely manner.  I also suggest that it be noted to be more vigilant when it is the very first day back in a training environment; as controllers could be rusty in a training environment.  It was also the first day back from X days off due to COVID-19; and these extending absences should be taken into account when managing workload for controllers.  As an OJTI and Controller; I need to be more aware of these things; and be better prepared to handle any traffic presented; but this was a very difficult task to accomplish given all of the factors mentioned above; specifically workload; complexity; training; and overall saturation.


Second narrative: On approach to ZZZ we were on vectors for a right downwind for Runway XXL at 10;000 feet. ATC issued us a descent clearance to 6;000 feet. The frequency was extremely saturated with aircraft and radio transmissions and it appeared as if ATC was training (there were two controllers working the frequency together). As my first officer was descending through about 9;000 feet I noticed an aircraft on our TCAS display that appeared to be climbing quickly towards us on a trajectory for our flight path. We began to shallow our descent and I queried ATC about the traffic. We received a TCAS TA 'Traffic; Traffic.' The Controller issued us a turn towards the east and told us to continue our descent to 6;000 feet. At this point we received a TCAS RA 'Monitor Vertical Speed' and shallowed out descent to level. I told ATC about that we were responding to a TCAS RA; and they asked us to report clear of conflict and resume the descent at that point.ZZZ TRACON was extremely saturated with traffic while we were on approach and had a layer of broken clouds at about 4;000-6;500 feet. I think this was potentially a VFR aircraft at 7;500 feet that was not talking to TRACON. TRACON seemed unaware of their position relative to our flight path.Good thing we have TCAS...ATC was completely unaware of this aircraft and continuously asked us to continue the descent even after we queried them about the traffic. We ignored them and followed the commands of the TCAS RA and avoided the conflict.


Synopsis: TRACON Controller and air carrier Captain reported an airborne conflict situation between the Captain's commercial aircraft and an unknown VFR aircraft.