B737 Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 166; Flight Crew Total 11027; Flight Crew Type 11027
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Took Evasive Action; General Maintenance Action
Weather; Aircraft
Started descent for the ZZZZ 1 arrival into ZZZ from FL400.  At approximately FL330 we received an IAS DISAGREE message. I checked all 3 airspeed indicators and mine matched the standby while the Captain's showed 10 KTS slow. Captain ran the appropriate checklists. Shortly after finishing the checklist we got an ENG master caution. I looked up and saw the Electronic Engine Control (EEC) had both reverted to ALTN. Captain ran the checklist. At approximately FL200 we got the ALT DISAGREE message; again ran the checklist. As we descended the Captain's airspeed indicator got as low as 40 KTS slower than my airspeed indicator and the standby airspeed indicator.  We continued to descend via the arrival and shot the visual approach to Runway XXL with no other issues or incidents.
B737 First Officer reported an airspeed split and Electronic Engine Controls both switching to alternate while in icing conditions.