Date: 201812
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Climb
Aircraft component: Horizontal Stabilizer Trim
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Flight Engineer; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport
Contributing factors: Equipment / Tooling
Primary problem: Equipment / Tooling

Narrative: Noted on preflight; a write up; for a cycling trim situation on the inbound leg. With no faults noted by maintenance; it was cleared. First Officer (FO) and I discussed the situation as one of the threats possible; with emphasis on being alert for the cycling trim situation to possibly repeat. Reviewed applicable procedure for a possible runaway trim scenario. Upon takeoff; Autopilot A was engaged at approximately 1;200 FT AGL. As flaps were retracted and airspeed began to increase; additional trim inputs were immediately noticed by both pilots. With flaps now up; FMC called for 250 KTS. Aircraft pitched to 260 KTS with trim inputs; then re-pitched to 240 KTS. The trim system would activate for 1-2 seconds and then immediately reverse itself; trimming in opposite direction. I directed FO to ask for intermediate stop on climb; where we then stopped at FL230. Advised ATC we were experiencing a trim system problem; but the aircraft was stable and trim stopped fluctuating once a stable and level pitch was attained. I chose not to declare an emergency at this time as we did have a stable aircraft; but contacted dispatch via radio; and informed dispatcher of the situation; that it was a reoccurring event; and that I was not comfortable taking the aircraft to ZZZ1 with a primary flight control system not operating properly. Therefore I would return to ZZZ. Dispatcher brought Maintenance Control in I believe at that point and I gave them a description of the problem. We then completed those calls; informed ATC of our desire to return to ZZZ; and no emergency being declared at this time. The trim problem immediately reappeared when given a descent to 11;000; executed via Level Change on the Mode Control Panel. I was flying and at that point disconnected the autopilot; and hand flew the remainder of the approach to the landing. No trim problems were noted with autopilot disconnected. Maintenance ACARSed us several times; requesting us to attempt to troubleshoot the failure and gather information. I elected to not do this. I knew I had a failed trim system and did not wish to engage a deeper problem if something else went wrong with the system while troubleshooting. In addition we [were] now under 15000 FT; in the terminal area; and I was hand flying the aircraft. Too many distractions; as well as a potential bigger problem if something else went wrong. We both put on the table the trim motor / elevator jackscrew failure a few years back that happened to another carrier. That situation was perhaps the final reason I did not want to troubleshoot the failure. We finally told Maintenance Control via ACARS. 'We are busy '; as they were now a distraction with their requests as we were near or under 10;000 FT. Aviate; Navigate; Communicate. That is what I start every brief off with a new pilot at the beginning of a trip.




Synopsis: B737NG flight crew reported a trim problem during climbout resulting in a return to field.