Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Weather / Turbulence
Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem
Aircraft; Weather
This flight was a planned departure from ZZZ to ZZZ1.  Weather was overcast; rainy with relatively calm winds and temperatures decreased during preflight from around 10C to 4C prior to departure. Pushback was delayed due to ramp congestion but only delayed takeoff slightly.  The Captain was operating as Pilot Flying (PF) for this flight.  The First Officer was Pilot Monitoring (PM).  Takeoff was uneventful. The departure was flown autopilot off.  While heading toward ZZZZZ and climbing at 280 KIAS; sometime after passing FL180 and climbing to FL230 in Instrument Meteorological Conditions (IMC); Boeing 737-800 aircraft experienced extreme airspeed indicator swings on both sides of the cockpit.  Indications wildly fluctuated between 300 KIAS down to 180 KIAS.  The PF asked the PM if his indications were normal and the PM responded that his indications appeared erroneous as well and he had an airspeed disagree indication. The pitot heat was verified ON. The autothrottles started to chase the airspeed fluctuations and were subsequently turned off.  PF maintained the climb power and pitch angle and asked the PM to get a higher altitude from ATC.  ATC responded with a 'standby for higher' response.  The PM attempted to select Vertical Speed and it would not engage.  All vertical guidance was unavailable.  The PF asked the PM for a groundspeed and the PM responded that he did not see one.  There was no groundspeed on the Captain's (PF) side as well.  The Standby Flight Instruments were difficult to read as they had been dimmed for the takeoff and now the sun was coming up. Simultaneously; we were approaching a turn from ZZZZZ to ZZZZZ1.  PF elected to maintain wings level and continued straight ahead as to not compound the problem by turning in IMC conditions with obvious airspeed errors.  Since the sun was just rising we could see the top of the weather was very close. As we approached FL230 we continued to climb and notified ATC.  ATC cleared us to FL380.  After reaching an altitude; probably FL240/FL250 in Visual Meteorological Conditions (VMC) the aircraft returned to nominal limits.  The flight continued under VMC to ZZZ1.  The aircraft flew normally after the event and landed safely.  Discrepancies were noted in the Aircraft Maintenance Logbook (AML) and maintenance personnel were debriefed by the Captain. Recommend a third air data inertial reference unit (ADIRU) on the B-737 so the bad ADIRU can be removed from the equation during a failure and still have a comparator feature.
Early morning departure out of ZZZ to ZZZ1. During climbout on the SID just after passing through the transition through FL180 I noticed we had lost the flight director and a yellow 'speed disagree' flag on the PFD (Primary Flight Display). I then looked at the MCP and VNAV/LNAV was off. Tried to re-engage and it wouldn't due to the PFD flag. About that time I noticed the speed had dropped from 280 KIAS to about 260 KIAS and we were off course having missed a slight turn on the SID. The Captain then said his was not right and asked me what mine said. I had said mine didn't seem correct either. Then he asked me what our ground speed was and I looked and mine was blank; not showing and wind/GS/TAS. At that time I told Center that we were having a problem with our instruments since we were off course and altitude. He came back and gave us present heading and FL230. The Captain then asked me to see if we could continue our climb since we weren't far from being on top of the weather; I asked and was told to stand by. A few seconds later Center gave us FL380. At this time I notified ATC having noticed we were getting further off our heading and the situation was getting worse. As we started to climb everything came back; air speeds matched; flag went away; was able to re engage LNAV/VNAV and flight directors. Few seconds after that we were on top in VMC. Everything came back just as quickly as we lost it. We were cleared to our next fix and resumed normal operations. We discussed our options and mutually decided that since there was clear weather for the rest of the way to ZZZ1 and everything was working that it was best to continue rather than turn back into the weather and return to ZZZ. The rest of the flight was uneventful and sent an ACARS message to let Maintenance know we would be writing the aircraft up when we landed. We landed in ZZZ1 and the Captain made the entry in the logbook when we got to the gate.
B737-800 flight crew reported Air Data Computer malfunction inflight.