Date: 201912
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Fog
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class C ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Workload; Time Pressure; Training / Qualification
Second reporter function: Pilot Flying; Captain
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: Taxi
Contributing factors: Weather; Human Factors; Company Policy
Primary problem: Human Factors

Narrative: While enroute to ZZZ on Aircraft X we observed an abnormal Number 2 engine vibration; we contacted dispatch and were told to return to ZZZ1. The return to field occurred uneventfully. We were assigned a new aircraft and re-launched for ZZZ. On the second flight; before we started our descent into ZZZ; we obtained the WX (ASOS); visibility was reported at ¼ sm (1600 RVR equivalent) and indefinite ceiling; we discussed our options and decided to execute a CAT II approach; we had a pretty strong tailwind; so the arrival occurred quite rapidly. To our surprise and due to our late arrival; we discovered that the Control Tower at ZZZ had already closed; approach control advised of low visibility at the airport as reported by another aircraft that had just landed. We set up the approach according to our established procedures (transferred control to FO; set and briefed the approach; monitored approach; etc...). The entire area around the airport showed scattered areas of patchy fog close to the ground; we could see the airport even though there was a patch of fog on top of the airport; we could see the runway lights through the fog. The CAT II approach was executed to the FAF and then the CA took controls and continued as a normal CAT I approach because visual conditions were adequate. We could see the approach lights and runway lights through the fog from the FAF. A safe landing was made and visibility on the ground was 1/2 sm. I failed to recognize the control tower was closed and that RVR reports are required for a CAT II (visibility reports only are not enough; actual RVR reports are needed) In the future I will ensure that all required items needed for the execution of a CAT II approach are operationally/available before starting this procedure.


Second narrative: I was PF and CA of Aircraft X ZZZ1 to ZZZ. Halfway to ZZZ we got an abnormal engine vibration of 4.0. I sent an ACARS message to dispatch and a little while later they replied they had talked with Maintenance and wanted us to return to ZZZ1. We were tankering fuel and returned to ZZZ1 with no further issues. We were re-dispatched with another airplane and took off again for ZZZ running hours late now.The weather forecast for ZZZ at our ETA was good; 6 sm visibility and BR; and we did not require an alternate. We also had a tailwind; approximately 50 knots. The weather came in about 200 miles from the destination; and my FO told me visibility was 1/4 sm and fog. Looking around we had excellent in-flight visibility and could see all the city lights on the ground below and several small areas of patchy fog. I checked to see if there was a Cat II approach available for the airport and there was. I told him we would set up for the ILS Cat II approach for Runway 16L; and we got to work. Workload was high as the tailwind and now unexpected Cat II procedure were factors added. We successfully worked to get ready for the Cat II approach; and as we got closer; we still had excellent visibility and ground contact. We were both confident we would land with no issues.When we got vectored to final; we could see the approach lights 10 miles from the airport. We could see a layer of ground fog over the airport and it did not look very dense. We were told to switch to advisory frequency and cancel IFR on the ground. That's when I realized the tower was closed. I decided to continue the approach as I could see the airport; runway lights and approach lights. I took the controls after passing the FAF and continued as a Cat I approach. Conditions were VMC all the way down to approximately 60 feet AGL. At 60 feet AGL we descended into shallow fog and made a safe landing with 1/2 sm visibility. We closed the flight plan; ran the checklist and continued to the gate with no further issues. The next morning I realized all the mistakes I made. I broke with company policy and initiated a Cat II approach without RVR reporting and an operating control tower. I failed to check the Tower hours of operation and did not pick up on the absence of the RVR reports. I have reflected on this experience and will be more cognizant of these requirements in the future.  I need to be more aware of the CAT II requirements to initiate the approach and hours of operation of control towers for every flight. Contributing to my overlooking the need for RVR reporting was that conditions were seemingly good all-around and I thought of what we needed to do to get in; rather than we can't legally do this. I likely would have looked at it more skeptically if conditions had not seemed so favorable. These favorable conditions contributed to allowing me to drop my guard and break with company policy.


Synopsis: EMB-175 Flight Crew reported non-compliance with company policy by executing a CAT II approach without available RVR reports.