Date: 202105
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: Mixed
Weather elements / visibility: Icing
Aircraft: B737 MAX 8
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise; Descent
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pitot/Static Ice System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Workload; Troubleshooting
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Overshoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: Takeoff and climb to cruise was uneventful. At cruise FL260; received ATC reroute to avoid weather. Reroute was ZZZ1 then back onto the ZZZZZ arrival. About 50 miles north of ZZZ1; we were cruising at 280 kts in IMC conditions at +2 degrees TAT with engine anti-ice on. The Captain was flying. We then noticed the airspeed start to go way down then go way back up. It indicated maybe 40 kts to 300 kts (unsure exactly). 'Airspeed low' kept announcing as well. The Captain turned off the autopilot and autothrottle and set 4 degrees nose high and told me to set power. I pulled the power to 70% N1 and we compared PFDs. My airspeed indications would indicate properly for a few seconds then jump up or down. The Captain's was constantly moving up and down so we transferred control to the First Officer. I called for the QRC and the Captain read and accomplished the steps (we had missed flight directors off). We had climbed a couple hundred feet during this and I asked the Captain to notify ATC and I turned the airplane eastbound in an attempt to exit IMC. It worked and a couple minutes later we exited IMC and started a descent to warmer air. While the Captain ran the QRH for unreliable airspeed and informed ATC/dispatch; I continued to fly. As the air warmed and as we exited IMC; airspeed indications returned to normal. We reviewed pitch and power setting in the QRH to make sure the airspeeds were accurate. The rest of the descent and arrival to ZZZ was uneventful. My guess is we accumulated ice on the probes enough to make the airspeed indications go unreliable. I didn't see abnormal icing on the windshield wipers nor was icing reported. Being in IMC at +2 degrees was about perfect conditions for it. After landing; the Captain and I talked about how we were thankful for 737 MAX simulator training we had both recently completed. The training prepared us so well for this and I am thankful to our check airmen in the sims. I felt well prepared for this as described above thanks to 737 MAX training.


Second narrative: On descent to ZZZ; Captain Pilot Flying; in IMC conditions; FL260; TAT +2. No visible icing. Engine anti ice on. Airspeed unreliable on Captain's side. Repeated 60-100 kt changes with aural 'airspeed' warning. Executed QRC/QRH. First Officer flew rest of flight. Notified ATC and notified Dispatch on ACARS. Notified Maintenance on the ground; wrote discrepancy into log book and discussed the occurrence in detail with the mechanic at the gate. [I] suspect icing; but had no indications of a fault in the pitot or air data systems.


Synopsis: B737 MAX 8 flight crew reported unreliable airspeed fluctuations during icing conditions.