B737-800
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Aircraft Equipment Problem Critical
Flight Crew Diverted
Aircraft
Departed ZZZ following radar vectors and assigned altitudes. We entered IMC (Instrument Meteorological Conditions) conditions and shortly thereafter we received erroneous readings on airspeed and altitude from both primary flight displays. I assisted the FO (First Officer) in attempting to keep the plane under control; but quickly had to take control of the plane due to large pitch changes taking place from bad information from the flight directors. After disconnecting the autopilot and auto throttle I was able to get level pitch and a thrust setting for straight and level. I was able to determine the standby instrument was the most reliable and used that while the First Officer ran the QRH (Quick Reference Handbook) for airspeed unreliable to maintain a safe level flight. There had been prior to me taking control altitude deviations of 2;000 ft. and the airspeed was rolling back on my PFD (Primary Flight Display) to speeds from 0-162 kts; while the First Officer's ranged from 250-320 kts.The flight exited the clouds and we were VMC (Visual Meteorological Conditions). To assist the First Officer; I completed radio transmissions. I demanded lower altitudes to remain clear of IMC conditions. Once below the clouds; I was able to work with the First Officer for completion of the QRH; setting up an approach; and completing necessary checklists. The speed brake would not arm; during the approach; so at touchdown I had to manually deploy the speed brake. This all happened very quickly and I never was able to formally advise ATC due to excessive workloads. I was provided priority handling by ZZZ Center and ZZZ Approach. The approach was a visual with a successful outcome.[Causal factors]; failure of one or both air data computers or associated systems. It is unknown by the pilot what those might specifically be.
B737-800 flight crew encountered loss of Air Data Computer in flight.