Date: 201810
Local time of day: 0001-0600
Location: SJC.Airport, CA
Flight conditions: VMC
Weather elements / visibility: 10
Light: Night
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Takeoff / Launch
Airspace: Class C SJC
ATC / advisory: TRACON NCT
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Situational Awareness
Second reporter function: Pilot Not Flying; Captain
Anomaly: Airspace Violation All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert
Contributing factors: Procedure; Human Factors
Primary problem: Human Factors

Narrative: The Captain and I were getting ready to push on leg 4/4; [out of SJC]; on what had become a pretty long day. The pushback crew was trying to establish communication; the Ops Agent had just given us our [information] sheet which said we had like 25 minutes left to get airborne without a waiver. We had started our first two legs each with mechanical delays; and now were roughly 2.5 hours behind schedule. I tried to get the latest ATIS for push and that's when I realized that people on Tower frequency were making CTAF calls. We were unable to get digital ATIS and had to tune it on the radio. The weather was VFR; 10 SM and clear skies. This made me scratch my head a bit as I hadn't expected the tower to close; although it was [late at night] local time so it was late enough. There were no specific instructions regarding a closed tower in the Dispatch Release and nothing in our CPDLC which I had gotten 15 minutes earlier while the tower was still open. It then occurred to me that maybe there was some info on the airport pages regarding CTAF operations. The only reference at all was regarding the curfew - all jet operations prohibited during curfew hours of [early morning period]. Delayed scheduled air carrier flights and alternate/emergency operations excluded from restrictions. That's when the Captain asserted that since we had our CPDLC clearance and departure frequency we should be good to takeoff and talk to departure. At this point I feel like fatigue was really hampering my decision making ability; because I had a little acorn of doubt in the back of my head that we needed to clarify what exactly we needed to do; but instead of discussing my doubt I just rationalized the Captain's reasoning as good enough and went with it. So we pushed back and I made CTAF calls that we were taxiing to the runway. Initially there was a regional aircraft landing; then a helicopter; and then it was quiet. We approached the hold short and we could see an aircraft on final which our TCAS showed at 5 NM. The Captain said he was going to keep it rolling and I made our final CTAF call announcing our departure saying that we were making a right turnout; but I flubbed the name of the departure. It was my leg so he gave me the aircraft and we took off uneventfully. We got the gear up; accelerated; and then at 1500 feet he gave Departure a call. Initially the Controller asked us to squawk identification and then I heard some excitement in his voice when he came back. I can't remember the exact verbiage but something to the extent of 'Aircraft X; you can't just take off into controlled airspace without a clearance...' That's when my heart sank. I kept flying the SID but I was mad at myself because I knew I had that nugget of doubt and I could have asserted myself to avoid this situation. As we checked out of NorCal's airspace the Controller gave us a phone number to call for a potential Pilot Deviation. Looking back at this situation; after having gotten some sleep; I saw a couple of factors that I believe played a role in this occurrence. First; taking off with a closed tower is something I have never done at Company. I've done it at previous jobs; but I always took off VFR and remained VFR; or got my IFR while airborne in VMC; but never from an airport with an overlying Class B airspace. At Company I have landed with a closed tower; but there were specific instructions outlined in the SIP for that airport which made it clear what we needed to do. In our situation; because of the delay; we found ourselves working late at night at an airport where we don't usually fly that late; and no amplifying instructions. I don't know why it didn't dawn on me to address with the Captain the fact that I'd never done this before at Company.Second; we had received our CPDLC while the tower was still open but nowhere along the way did we realize; or did anybody (Dispatch; Clearance; Tower; etc.) tell us; that the tower would be closed upon departure.I actually had to call Tower and ask them to resend my CPDLC because it dropped out of our box. He said ok; and did so; but didn't mention he would be closing soon. I'm in no way trying to shift any blame; but it seems that somebody could have given us a heads up. Who knows; maybe tower did try to call? I wasn't actively monitoring them on the speaker so I don't know if they did. Third; as I mentioned before; I was tired and that impacted my ability to scrutinize this situation. We had been on duty for roughly 10 hours at this point. I was up early with my family and was running on fumes at this point in the night. As we were arriving into SJC the Captain and I were discussing our fatigue level; but neither of us said that we were unfit to continue. Maybe a bit of 'get-there-itis' paired with 'we can make this happen.' I've read all the stats that are put out about fatigue; and I know they're true; but honestly I've just not had all that many situations where the effects of fatigue have caused something like this to happen to me. It's pretty eye opening and I feel like we really should have talked more about it as a crew.Fourth; I should have been more familiar with information available to me from Company publications. After the fact I have since gone back and found where this situation is discussed in the FOM. I had never read it before. While it does state clearly that we needed to get a clearance time/void time; we didn't necessarily fit the exact parameters of either paragraph regarding closed tower operations; and the airport pages had no amplifying information; but; it is something that I could have been more familiar with. Additionally; although what we did was not directly in line with the FOM; I'm still not exactly sure if/how it was illegal. As far as I know we took off from Class E airspace in VMC and contacted ATC at 1;500 feet; never entering any controlled airspace. Lastly; and I've already fessed up to this; but I should have spoken up; plain and simple. There was that little bit of doubt in the back of my brain that said something wasn't quite right here but I chose to bury it and press. Being more assertive and a better communicator could have easily stopped this bit of Swiss cheese from aligning and allowing the outcome. A call to Dispatch or to NorCal would have been easy enough; and free; and I wouldn't have to spend all this time discussing my day.


Second narrative: Arriving SJC was uneventful. Prior to departing SJC; the First Officer called ATC to resend our pre-departure clearance as we did not receive it via CPDLC. They resent and we received it immediately. Very soon thereafter listening to the Tower frequency at push time we realized the Tower was now closed as we were hearing traffic advisories from GA aircraft in the pattern and on the airport at SJC. For us; the Crew; it was the middle of the night. We were 11.5 hours into our duty day with one more leg to fly. Any more delays and we were encroaching on duty limits. I had searched the SJC SIP and there were no references to the Tower closing. There is a curfew mentioned from 2330-0630 local time for aircraft operations with an exclusion for delayed air carrier flights. Finding no references for departing when the Tower was closed it was my intention to depart VMC and obtain our clearance with NorCal on departure. We made Traffic Advisories for our pushback; taxi; and takeoff. As PM I contacted NorCal at 1500 feet. He was not happy to say the least. He said we could not depart without a Release. I mentioned the Tower was closed. Again it was my intention to depart VMC and obtain our clearance with NorCal on departure. He was still obviously not satisfied with this.Handing us off to OAK Center; he gave me a phone number to call for 'possible Pilot Deviation.' I called the number when I got to my hotel room. The person on the other end stated the same that we needed a Release before departure. He took my name; Pilot Certificate number; phone number; and home address. I used to do this previously at another air carrier quite frequently with no issues whatsoever. And yes it was many years ago. Once you dig it up; in our FOM states that yes we do need to get an IFR clearance (to include VOID time) from FSS; Departure Control; or En Route Center via telephone or radio. The very next paragraph same page; Departing VFR states that yes we can depart VFR provided we have VMC; maintain VMC on departure; and obtain clearance as soon as practical but no farther than 50 NM from departure airport. After sifting through the FOM in the quietness of my room I realize I should have obtained a void time through SFO Radio or other means. Clearly; in the heat of the battle; it was not so clear. The paragraph I could recall is the one that allows departure in VMC conditions and obtaining clearance with Departure Control. I would like to conclude this with my observations and suggestions. (Next paragraph-Preventative Measures) Please do not take this as finger pointing or deferring blame/fault in any way at any level. The blame /fault rests entirely with (ME) the Captain's Responsibilities.


Synopsis: B737 flight crew reported departing SJC after the tower had closed; but without a release form NorCal TRACON.