B737-700
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 300; Flight Crew Type 10200
Time Pressure; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Human Factors
En route ZZZ to ZZZ1 on (date) at cruise; we experienced a failure of our automation (FD (vert); autothrottle; and autopilot); indications related to temperature and vertical profile planning in the FMC. On climb; out of approximately FL 280 we witnessed the #2 thrust lever advance approximately a handle width or two to maintain N1 demand. It returned to normal shortly after. We discussed a possible EEC loss from that issue. After we leveled off at FL 350; the First Officer announced that he had lost the autopilot; flight director vertical guidance; and the autothrottle was displaying 'ARM'. We divided the duties at that point; agreeing that he would fly the aircraft and talk on the radio; and I would start working on the resolution; coordination.  ATC was notified of our equipment loss; per RVSM requirements. I checked circuit breakers; attempted to use other autopilot; and reviewed QRH to see where we might have some guidance and started ARINC connecting us to Dispatch/Maintenance Control. The First Officer and I were continually checking in with each other to ensure he had my updates on what I was finding; and to ensure that we were backing each other up on the raw data/hand flying of the aircraft. After speaking with Maintenance; I had to make the decision to stop the conversation due to the fact that we weren't getting anywhere with the troubleshooting; and we were getting time compressed for descent into ZZZ1.  Dispatch confirmed that we had visual conditions for landing ZZZ1 (post front passage on a significant weather day); so we continued to ZZZ1 vs diverting to our alternate of ZZZ2. At this point the First Officer had been hand flying for a while; and to prevent fatigue; I switched to the PF role as we started descent for landing. I asked the First Officer to back up my investigation of possible issues and try to narrow down what the source issue could have been. From what we had available; we believed we had lost 'air data' (TAT; etc.)  One thing of note was that the N1 required for 280 knots at FL 300; seemed very high. (87-88%). We examined if we had missed the EEC's going to soft alternate; they hadn't. We questioned whether the loss of air data inputs would have triggered the switch to soft alternate. It hadn't. Probe heat was functional; lights checked; breakers in.  At the point we failed to get consensus or guidance from Maintenance; we decided we would 'Fly it like a -200' and focused on good PF/PM communication; instrument scan; and attention to contingency plans. We landed uneventfully in ZZZ1; and after discussions with Maintenance Control; we agreed that the loss of TAT (Total Air Temperature) was likely our primary condition impacting our flight. We noted that we had no QRH; or trained procedures to fall back on; but given our automation policy and basic proficiency; we were quickly pointed to flying the aircraft; navigating with our fully functioning FMC/NAV; and communicating with our Team; we safely brought our event to a close with no impact to the flight; and no concern being brought to our passengers.
While flying from ZZZ to ZZZ1; we had an automation failure; while in cruise at FL 350. The Autopilot reverted to CWS-P (Control Wheel Steering-Primary) and autothrottles reverted to ARM.  Shortly prior; while climbing through FL280 we noticed the #2 TL was about 1-2 inches higher to hold the same N1s which seemed peculiar and we both noted at that time that we may have had an EEC reversion to soft alternate. During the discussion the TLs matched again with the A/T. When the automation failure occurred I was PF and guarded the yoke and A/Ts while we began to diagnose the issue. The C checked circuit breakers and switched autopilots and reset FDs but this did not fix the issue. I continued to hand fly and talked to ATC while the Captain checked the QRH and called Dispatch. We got a lower altitude for a better buffer limit/accountability and to get out of RVSM airspace. While the Captain was on the radio with Dispatch and Manager on Call; we also noted that we had no TAT indications and there were dashes above the N1s and CRZ/CLB was not visible for TL settings. This led us to believe we had some sort of data failure. After the Captain completed the call to the Company; we decided that we could not diagnose any further and the only guidance was to hand fly the aircraft from this point. We transferred control to relieve me of flying and to spread the duties for better RRM.  After the Captain took control of the aircraft I double checked the QRH; AOM and looked in the FRM for guidance on TAT indications; A/T; and EEC systems. At this point we prepared for a day VMC; landing in ZZZ1 and asked ATC to give us a long final and vectors to the final for added situational awareness. The Captain made a good approach and landing in ZZZ1. At the gate the Mechanic did a byte check and other troubleshooting and we were informed that it was a TAT failure.
B737 flight crew reported loss of Multiple systems during cruise that was surmised to be caused by loss of Total Air Temperature and continued on to land uneventfully at destination airport.