Date: 202103
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: B737 MAX 8
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Horizontal Stabilizer Trim
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Time Pressure; Workload; Situational Awareness
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed As Precaution; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Out of an abundance of caution and to the best of my memory I can recall that shortly after the initial climb and in a clean configuration the Captain alerted me that he had some difficulty with the electric trim on his control yoke. I observed that it was indeed intermittent. After I completed the Climb Checklist we tried some trouble-shooting with both autopilots and my trim switch. With no caution lights; I referred to the QRH to help diagnose the issue with the proper checklist. During this time the Captain was contacting Dispatch and Maintenance for assistance while I talked to ATC. At some point in this process we were able to notice that my autopilot would engage and I became the Pilot Flying. We stopped the climb and slowed the aircraft. The Captain proceeded with the Stabilizer Trim Inoperative Checklist which calls to cutout both stab trim cutout switches and manually trim the aircraft. As I flew manually we elected to advise ATC and return to ZZZ. The Captain informed the Company; ATC; flight attendants and passengers and offered his assistance to me. I vaguely recall that during the descent a Speed Trim Fail light illuminated as a result from the cutout switches being selected to cutout. There was some discussion that we may or may not be over the max landing weight upon arrival and therefore an AML entry was entered after landing along with a Speed Trim Fail; Stabilizer Trim Failure; and inoperative autopilots entries. I performed a safe Flaps 15 landing [and] all passengers and crew deplaned safely with no injuries. I can attest that the training I have received was very beneficial to the successful outcome from this event. I believe as a crew we worked the problem out very well with the strategy and am thankful for the Captain's knowledge; professional conduct; and reassurance to everyone for a safe outcome. The mechanic did state that perhaps the event may have been caused by a software issue.


Second narrative: During climbout and after cleanup; I noticed that the electric stabilizer trim was intermittent. Then it became unresponsive. At this point the Speed Trim system appeared to actuate for about half a second and never actuated again. We attempted to engage the A autopilot. It wouldn't engage. The B autopilot did engage and I passed control of the aircraft to the FO (First Officer). We conducted the 'Stabilizer Trim Inoperative' checklist. Within about 5 minutes of engaging the B; it disengaged itself and the FO hand flew the aircraft for the remainder of the flight. We advised ATC and returned to ZZZ. We selected Runway XX and requested a 15 mile final to get fully configured and trimmed as well as possible. The FO was able to manually trim the aircraft without difficulty. During the descent; at about 12;000-15;000 feet; the 'Speed Trim Fail' light illuminated. We conducted a Flaps 15 landing and taxied back to the gate. I made an AML entry for the Stab Trim; Speed Trim Fail light and for possible overweight landing.I think the focus of the MAX simulator session was helpful in dealing with this situation.

Second callback: Reporter stated they were unable to manually trim the aircraft until the trim cutout switches were engaged. Post flight; it was learned that the electric stabilizer trim  failure was possibly due to a relay which had failed.

Synopsis: B737 MAX 8 flight crew reported a stabilizer trim issue that resulted in the autopilot disengaging during climbout. The flight crew elected to return to the departure airport.