Air carrier first officer reported pitch control problems after takeoff due to a trim switch failure...

Attributes
ACN	1618516
Time
Date	201902
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	Widebody Transport
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Elevator Trim System
Person 1
Function	First Officer
Qualification	Flight Crew Instrument Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

On taxi out; the ca's (captain) trim switch was tested per the MEL and was used to set the takeoff trim. After takeoff on initial climb out; the ca attempted to engage the autopilot without success. However shortly after that; the ca verbalized that his trim switch was also not working now. Ca was using considerable forward pressure to keep the nose down and ultimately had to pull the power back to better control the aircraft. We quickly agreed we needed to return to ZZZ due to controllability concerns. Ca continued to hand fly while I coordinated with ATC and set up for an otherwise uneventful return to landing at ZZZ.[station maintenance] was able to duplicate the problem on the ground after the event. The faulty first officer (first officer) trim switch was locking out the ca's trim switch and tripping the autopilot.

Original NASA ASRS Text

Title: Air carrier First Officer reported pitch control problems after takeoff due to a trim switch failure.

Narrative: On taxi out; the CA's (Captain) trim switch was tested per the MEL and was used to set the takeoff trim. After takeoff on initial climb out; the CA attempted to engage the autopilot without success. However shortly after that; the CA verbalized that his trim switch was also not working now. CA was using considerable forward pressure to keep the nose down and ultimately had to pull the power back to better control the aircraft. We quickly agreed we needed to return to ZZZ due to controllability concerns. CA continued to hand fly while I coordinated with ATC and set up for an otherwise uneventful return to landing at ZZZ.[Station Maintenance] was able to duplicate the problem on the ground after the event. The faulty FO (First Officer) trim switch was locking out the CA's trim switch and tripping the autopilot.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.