Date: 202102
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent; Cruise
ATC / advisory: TRACON ZZZ
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: Check Pilot; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Physiological - Other; Workload; Time Pressure; Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Staffing; Airspace Structure; Environment - Non Weather Related; Human Factors; Procedure
Primary problem: Procedure

Narrative: The FO was on the very first leg of OE. The flight proceeded perfectly until arriving in the ZZZ1 [airport] terminal area. ZZZ Center descended us and never handed us over to the local [ZZZ] TRACON. Instead; we were told to expect holding instructions. It was clear the Center Controller was very busy (he was doing an exceptionally good job). Instead of issuing holding instructions we were asked where we wanted to hold. We told him we wanted to hold at ZZZZZ [Intersection]; the initial approach fix for the ILS Runway XX to ZZZ [airport]. He issued instructions to hold south. We asked if we could hold north inbound; right hand turns. He issued instructions 'cleared as requested' with no EFC. He asked how much fuel we had onboard and we replied 2 hours. I didn't push the EFC because it was clear he was saturated and we were holding at 11;000 feet above a lower layer in VFR conditions. ATC explained to other aircraft that ZZZ [TRACON] was ATC Zero and he was the only Controller handling all aircraft going into and out of 4 controlled fields. It was difficult to simply get a break on the frequency so I decided to just be patient.We had been sending ACARS messages to the company enroute and didn't get any responses; this is not that unusual; usually Dispatch will reply with 'OK' but not always. When we were issued holding instructions we sent Dispatch an ACARS message 'Holding at OM for Runway YY ZZZ; no reason given' and once again; we did not receive a reply. Incidentally; I instruct all my OE pilots; as I did in this instance; to look for the 'VHF IN PROGRESS' display after selecting SEND on an ACARS message to be certain the unit actually sent the message. In all cases it did.The airport pages indicated that ZZZ2 [airport] was just XX miles away and we knew they were not affected by this situation. The weather at ZZZ2 was also good. Our FMC fuel reserve was 4.0 since we had no alternate. At first I wanted to use 7.0 as a decision point on fuel. My thought it would probably take 20 minutes to get to ZZZ2 if needed and I wanted a cushion so I added 3.0 to the FMC fuel reserve to make my decision. If we hit 7.0 on the fuel it would be time to contact Dispatch and go to ZZZ2. While we were doing all this ATC was relying on us to contact aircraft going into and out of the airports below to issue instructions. Needless to say we were a bit busy. We were told to descend first to 8;000 feet in the hold; then to 6;000 feet. On several occasions VFR aircraft popped up on our TCAS (no alerts were issued) as we were holding in Class E airspace above the ZZZ Class D and the ZZZ1 Class C. We were keeping a keen eye outside. At one point ATC issued instructions to climb to 8;000 feet in the hold for traffic. Again; the Center Controller was doing an exceptionally good job. We were told on several occasions what our sequence was going into ZZZ; third; then second; then next.  Our intent; of course; was to get into ZZZ safely.ATC was issuing phone numbers for aircraft to call when on the ground. I was a bit confused as to why; I thought the towers were open; but paid it no mind. We heard the Controller mention COVID as the reason to another aircraft. Unfortunately; the aircraft landing ZZZ in front of us; Aircraft Y failed to call the phone number. This haunted ALL landings into all 4 airports. The Controller explained to another aircraft that his procedures precluded him from clearing any other aircraft for approaches into any of the four fields until had had a cancellation from the Aircraft Y. In fact; ATC had us attempt to call him on the frequency.I considered whether we could get in VFR but we could not get down into the class D with ZZZ Center and there was a layer between us and the field (I've forgotten where it was but probably about 3;000 feet). I then considered our fuel considerations; rather than using the 4.0 FMC fuel reserve I decided to use the actual FAR fuel reserve of roughly 3.6. The FO stayed on top of duties not only contacting other aircraft but complying with my requests as the flying pilot very well. Finally; when we reached 6;600 pounds of fuel remaining I asked the FO to contact Dispatch via ARINC phone patch. We had already looked at the ARINC Services page in the Jepps early on and determined that ARINC had a surface on ground frequency of XYX.XZ at ZZZ1; and we would be able to get a hold of them down low. I asked FO to come up with a diversion plan. FO worked with Dispatch who recommended ZZZ2 (of course) and said the fuel required would be 1;100 pounds at 10;000 feet. This seemed too low; I didn't see how we could climb to 10;000 feet; fly XY miles; and shoot an approach and landing on 1;100 pounds (and change) of fuel; so we declared minimum fuel and requested an immediate direct vector to ZZZ2. At no point did we use the words 'Mayday' or 'Emergency'. We were instructed to fly a heading (I believe it was 045 degrees) and issued climb instructions to 10;000 feet. We immediately complied and began to set up for an approach into ZZZ2.The FO did a great job juggling responsibilities; getting ATIS and setting up for the approach; contacting ZZZ1 local; etc. At one point ATC queried our fuel status and the FO initially used the word Emergency but then quickly corrected and said we had declared Minimum Fuel. We landed on ZZZ2 Runway XXL with 3.7 on the fuel. We pulled off the runway and asked ATC for a position where we could sit and call the company.We called Dispatch on the cell phone and were instructed to go to the 'Maintenance Ramp.' We complied and were met with a follow me car where we parked; right next to an aircraft with a full load of passengers (obviously there for the same reason; we were later joined by another aircraft). We were immediately met with a set of stairs and a representative who asked what we needed. Dispatch immediately gave us a field load and we ordered thirteen thousand pounds of fuel. We arranged for the proper fuel load. It took some time for the fuel truck to arrive.We then had to coordinate getting paperwork to the aircraft. While Dispatch and the team did a great job of getting that all set up; the young lady driving back and forth had to go quite a ways to get our paperwork which took a great deal of time.Once we had our paperwork we were able to depart for the short flight to ZZZ. We completed the legs without further incident.I am uncertain what drove ZZZ TRACON to close; whether it was a scheduled cleaning due to COVID or some type of emergency. We reviewed the ATC and FIR NOTAMs and did not have anything mentioning the closure. Clearly this was the beginning of the delay. Then; it was further exacerbated by the crew of Aircraft Y jet failing to call the phone number after landing. Had they called we were next to be cleared to land and we would not have diverted.Several suggestions: We need clear and concise ACARs policies in the FOM. Each and every time Dispatch receives a message from a crew inflight they should ALWAYS reply. Perhaps this is a policy with Dispatch; but since it is not in the FOM and once in a while we do not hear from them we have no idea and I was not concerned about not getting replies; until we mentioned holding to them and I got no reply. That's when we hopped on the ACARS Services chart and noted that ZZZ1 had a ground based frequency and we could reach them from our holding position (incidentally; many of our pilots don't even know that table exists). Second; It is not unusual for ACARs not to work. This needs to be cleaned up. We are constantly writing up aircraft for 'NO COMM' and ACARs failures and they don't work. Honestly; I'd say ACARS works correctly about 2/3 of the time; certainly not the spirit of FAR 121.99. Granted we have ARINC; but crews will rely on ACARS just to find out after the fact that dispatch never got anything from us. Next; if this was a scheduled COVID cleaning we should have known they were going ATC Zero before we arrived in the terminal area. Dispatch was even caught off guard about it. ATC must develop a means of communicating this so we don't find out so late in the game. They should also consider issuing a TFR. Perhaps the FAA should consider a new type of TFR for COVID. Frankly; I am a small aircraft owner and use it frequently. I don't want to be told I can't fly over class D airspace while in Class E airspace simply because they are cleaning TRACON. On a beautiful sunny day there are going to be aircraft all over. If I were flying GA in the area and knew the TRACON was down I'd probably stay away just because I don't want to get run over by a transport. Finally; the company should consider what paperwork we REALLY need at the aircraft. For instance; we can already get performance via ACARS. We can pull up our NOTAMS on our tablet. That would leave signing fit for duty and the release. Perhaps we could give Dispatch all the pertinent info (they already had the ZFW weight and balance) so all they needed was fuel onboard and they could simply give us the necessary numbers for departure. Next; send us an ACARS message for signatures - we could print 2 of them and leave one with the rep on the ramp. Had we been able to do that we would have been out about an hour earlier and would NOT have taken another delay. Incidentally; we obtained our PDC via ACARS in ZZZ2 correctly and it worked properly all the way back; including the summary page.




Synopsis: Air Carrier Captain reported the unannounced closure of a TRACON that was possibly due to an 'ATC Zero' event caused a divert for fuel. Captain reported there was only one ATC Controller working multiple positions.