B737 MAX 8
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Procedure; Aircraft
IAS Disagree followed shortly by a ALT Disagree; autopilot disconnect. Complied with IAS Disagree Quick Reference Handbook. Informed ATC would not accept a descend via clearance or airspeed closing restrictions. Let them know we would slow and configure early to determine safety. At some point before doing the normal descent checklist the Engine Electronic Controls (EECs) went into ALT. We discovered this during annunciation test because there was no Master Caution; only ENG light during test and then looking at overhead (this system is archaic). The IAS and ALT Disagrees were intermittent even with EECs in ALT continuously. Landing uneventful. Informed Maintenance Manager; [local] Maintenance and submitted a report. Captain standby; ground speed and ATC ground speeds were close while First Officer's Airspeed and Alt appeared inaccurate. First Officer ran QRH - good job. Captain flew and communicated with ATC.
Reporter stated the pitot/static systems and the ADIRU were inspected and tested.  Reporter suspects the IAS and altimeter disagree were pitot/static related but does not have direct knowledge of that.  Reporter stated the EEC ALT issue is probably separate from the IAS and altimeter anomalies.  Aircraft is back in service and reporter is unaware of any further problems with this particular aircraft.
B737 MAX 8 Captain reported that the First officer's airspeed and altitude indications became unreliable in cruise; along with both of the Engine Electronic Controls switching to Alternate and elected to have ATC assist with descent and approach.