Date: 202108
Local time of day: 1801-2400
Location: ZZZ.Tower, US
Light: Night
Aircraft: B737 MAX Series Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Mach Trim
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown; Confusion; Situational Awareness; Time Pressure; Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport; Flight Crew Overcame Equipment Problem; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Human Factors; Aircraft; Environment - Non Weather Related
Primary problem: Aircraft

Narrative: Upon departure and climbing through 1;500 feet MSL; a Master Caution followed by Speed Trim on the overhead panel alerted us during the acceleration phase from flaps 1 to flaps 0. Shortly thereafter; I believe the autopilot tripped off or I disengaged the autopilot leaving me to manually fly the aircraft. It was then I noticed that my control wheel trim switches were not working. I asked the FO (First Officer) if his control wheel trim switches were working; and he said NO as well.It was then I extended the manual trim handle and proceeded to manually trim the aircraft. I also asked the FO to set speed to our current speed (approximately 210 knots) so to minimized as much trimming as possible. I then asked what Master Caution light illuminated; and the FO responded it was associated with the Speed Trim Light. I then called for the Speed Trim Fail Checklist in the QRH. The FO completed the Speed Trim Fail checklist; but there was no further direction in that checklist other than to continue normal operation. Nothing led us to refer to any other checklist such as Stabilizer Trim Inoperative due to our electric trim was not working.I then asked the FO to look and see if there was an Electric Trim Failure Checklist; because we did not have a jammed stabilizer nor a runaway Stabilizer Trim and the aircraft was flying just fine with the manual trim wheel. With me flying the aircraft and the FO trying to assist with ATC; QRH; while trying to assess the true problem; it apparently created a scenario where he simply overlooked the Stabilizer Trim Inoperative Checklist Condition statement.I was busy hand flying the aircraft; and with the distractions of talking to ATC and keeping the aircraft in trim; I did accidentally allow the aircraft to descend as much as 400 ft. below our assigned altitude of 3000 ft. MSL; but recovered quickly before ATC inquired. After realizing the additional task loading we were creating on ourselves; I elected to return to ZZZ without further troubleshooting. This set in motion a different set of task priorities for the FO in order to coordinate our return with ZZZ Operations and Maintenance. We evaluated our landing weight to be below MGLWT (Maximum Gross Landing Weight) and the only other immediate concern at the time was getting a longer final so we could get the aircraft configured and trimmed without getting behind in controlling the aircraft again.Once we caught up with our duties and were turning on final; I inquired again with the FO as if we had forgotten any possible QRH checklist for our condition. He again confirmed he could not find anything else in the QRH for Electric Trim Failure. That didn't sit at ease with me; as having recently completed the MAX training of runaway stabilizer. I remembered hand flying and trimming the aircraft and there was also something specific with the flap setting chosen; I just couldn't remember at the time. Even selecting flaps 30 for landing; something was still concerning me that I briefed the FO that in the event of the go-around; I may need help trimming the stabilizer through the configuration changes. The landing went uneventfully and taxiing back I still had that feeling we forgot a checklist in the QRH. After reaching the gate we verified; along with the Mechanic; that the electric stabilizer trim was indeed inoperative. I then had time to reach for the QRH myself and search through the checklist choices. It was then I found the Stabilizer Trim Inoperative Checklist; where the Condition and Objective statements under the title clearly stated and matched what our situation was.When I showed the FO the QRH Checklist for Stabilizer Trim Inoperative; he said he completely missed that as he was looking for something about Electric Stabilizer Trim Fail as I had called for; since the Manual Stabilizer Trim was working just fine.In the heat of the moment; sometimes confusion can take place and miscommunications can be amplified. In this case it was a Speed Trim Caution Light that lead us into the QRH; but in a correctly identified non-normal would of kept us into the QRH until all the proper checklists had been completed in this scenario. I recommend [adding] to the Speed Trim Fail Checklist a step prior to '#1 Continue normal operation.' I would word it (Condition: If stabilizer does not respond to control wheel electric trim inputs: Go to the Stabilizer Trim Inoperative checklist on page XX.)




Synopsis: B737 MAX Captain reported a Speed Trim Failure event.