Air carrier flight crew reported loss of several systems in cruise that required a diversion due to the inability to continue the flight as planned in forecast icing conditions.
Synopsis
Air carrier flight crew reported loss of several systems in cruise that required a diversion due to the inability to continue the flight as planned in forecast icing conditions.
Narrative
During cruise flight approximately four hours after departure at FL330 the First Officer (FO) and Relief Pilot were operating the flight. There was a loud bang behind the Captain's station; the Relief Pilot; and I both swung our heads to the back of the airplane; thinking that something had fallen. As soon as we did that; we received a master caution; followed by auto throttle's disconnecting. Immediately after that; we lost both FMCs and associated maps on our NDs (Navigational Displays). I disconnected the Autopilot immediately; because aircraft started to wander because it had no idea where it was. I quickly selected heading mode to at least maintain some semblance of navigational control of the aircraft. Almost simultaneously; we received EICAS messages 'HEAT P/S CPT' and 'HEAT L TAT'. Literally the first thought that came to my mind was that because of the loud bang; I thought the Captain side pitot tube had departed the aircraft. The sound seem to emulate left rear of the Captain's station. Both me and the Relief Pilot's heads snapped in that direction when we heard the sound. We got the aircraft situated in heading mode and re-engaged the Autopilot. The auto throttles were still not available. We ran the appropriate checklists for the two items that we had. For both of the messages; it did not allow for flight into ice and conditions. After running the checklists; I contacted flight control and had maintenance join us during the conversation. The FO now was back on the flight deck and discovered a circuit breaker that had been popped. We were able to re-engage the auto throttles; and the FMC's came back to life; so we had navigation once again. We reengaged LNAV. We essentially had a good airplane again; although there was a long list of items on the status page. We discussed them with the dispatcher and with maintenance and felt we could continue our flight safely. About 30 minutes after the onset I felt the aircraft was in a good state and could go back and take a short break. I was in the bank for approximately 10 minutes when one of the crew members chimed me to come back to the cockpit. I came up front and found that the FO and Relief Pilot had just opened up the checklist for airspeed unreliable. The Relief Pilot was in my seat and was hand flying; they did an exceptional job starting the procedure. I let them stay in the seats because the aircraft was in control and thought I would just help go through the checklist with them. We completed the checklist and discovered that the Captain side airspeed indications were erroneous. After I had gone to the back; they flew through some light cirrus clouds.Something they thought was completely benign and apparently it was enough to clog the captain side pitot tube. After the aircraft was situated; I got into the captains seat once again; and contacted Dispatch and Maintenance. Person A also joined us in the conversation. Essentially we were being told that we could not go to our destination because of icing in route. We also were told that we could reset the circuit breaker; something elected; not to do only because of the loud bang that we heard prior to the first event. I had no idea what that was; but I knew that it was somehow associated with what was going on. We came up with a plan with the Dispatcher to divert to ZZZZ. We had not declared an emergency; we had an airplane that was flying well; and didn't feel that it was necessary. The dispatcher discussed in detail with me our options. We thought ZZZZ would be a good choice because of the weather and having maintenance available. The most difficult part of the diversion was that nobody was expecting us; and the Dispatcher could not get over flight permits. Everyone that we talk to on the radios wanted to know why we were diverting; we just told them it was a maintenance issue. Once in ZZZZ's terminal area; we requested along downwind because we knew that there would be a possibility of a long extension time forflaps 1/5. When we extended flaps; we did receive the EICAS message 'FLAPS PRIMARY'. We followed the procedure for airspeed unreliable and requested performance data based on that. The landing was uneventful; crash rescue was standing by; although we did not request them.
Second reporter narrative
I had first break and had just come from the bunk to the cockpit. The Captain and Relief Pilot quickly informed me that they had heard a loud bang and had EICAS messages displayed HEAT P/S CAPT and HEAT L TAT along with a list of status messages. Captain called Operations/Maintenance on the SATCOM and I looked over the circuit breakers and discovered AC3 popped. Maintenance pinged the aircraft and asked if we had status message ELEC TR UNIT 3 displayed; which we did. They suspected this to be the issue. After talking with Operations/Maintenance we all agreed the flight could safely continue. The Captain got up to take a break and asked us to message our Dispatcher about any weather enroute because we would have to avoid icing conditions. About 10 minutes later we received airspeed unreliable after passing through a very thin cloud layer in cruise. We alerted the Captain and ran the check list. Relief Pilot was in the Captain seat and did an excellent job flying the aircraft. We established that the Captain side was unreliable and airspeed was slowly decreasing 7-10 kts. Once checklist complete ATC asked if we still needed pan pan and we cancelled it. Captain got back in the seat and we called Operations/Maintenance again on SATCOM and the decision was made to divert to ZZZZ. The neighboring countries aren't the easiest airspace's to divert through; we informed each sector that we were diverting for mechanical issue. There was a little confusion between controllers when we would get passed off to the next sector; however both were helpful in assisting us with clearances through airspace with no permits. We held briefly just outside ZZZZ's airspace while waiting on clearance to enter. While being vectored for ILSXX we received FLAPS PRIMARY and followed the procedure allowing extra time for flaps 1-5. Good landing and uneventful taxi to parking.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.