Date: 202110
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B737 MAX 8
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: TRACON ZZZ
Aircraft component: AHRS/ND
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Situational Awareness; Distraction
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural MEL / CDL
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: MEL; Company Policy; Aircraft
Primary problem: Aircraft

Narrative: While in the descent in a B737 MAX 8 ETOPS aircraft for a visual approach to ZZZ Runway XX; we noticed that the First Officer side EFIS Control Panel MINS (RADIO/BARO) rotary switch was malfunctioning. We had set our 'minimums' on both EFIS panels to the ZZZ Runway XX TDZE of 50' for the Visual Approach. We noticed that the First Officer BARO digital number was increasing on the PFD incrementally by itself. When the First Officer attempted to reset the BARO quantity to 50 feet; the First Officer BARO digital number began decreasing incrementally by itself to negative numbers. The rotary switch 'centering spring' (the functionality that centers the rotary switch to the neutral position) had apparently failed. As a result; we could not consistently set the First Officer BARO digital number to the desired TDZE of 50 feet and have it remain at 50 feet.I wrote up the discrepancy in the Maintenance logbook. When I contacted Maintenance Control; we learned that this particular discrepancy ('fault') is MELable in the NG aircraft; but it is not MELable in the MAX aircraft. I asked the Maintenance Controller if he had seen this discrepancy ('fault') before. He claimed that it is somewhat common in the B737 MAX. Since this is a 'Safety of Flight' issue (BARO minimums setting changing unexpectedly and unpredictably on its own); can Flight Standards consider putting a Bulletin out to the pilots to caution them of this anomaly; until the manufacturer of the EFIS control panel can do an engineering investigation and correct the tendency of the B737 MAX EFIS control panel; to occasionally have this 'Safety of Flight' discrepancy ('fault')? Can you please provide me with feedback on this issue? During an IMC instrument approach to minimums; this situation of the EFIS control panel MINS (RADIO/BARO) rotary switch malfunctioning (MINS number increasing or decreasing unexpectedly) could cause the pilots to receive inaccurate minimums information resulting in unexpected contact with terrain (e.g.; crash landing).   Company needs to publish [a] bulletin to notify pilots of this potential problem. Manufacturer Boeing Engineers need to troubleshoot cause of the problem and correct the problem.




Synopsis: B737 MAX 8 Captain reported the EFIS Control panel malfunctioned preventing them from setting the correct Touchdown Zone Elevation altitude. The reporter stated this is a recurring issue on the MAX 8 aircraft and could pose a safety of flight issue.