Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 160
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft; Procedure
On climb out; aircraft nose pitched up more than normal and I was pushing nose forward and trimming down. I noticed the trim was not moving on the trim tab indicator. I had the First Officer attempt to reset stab and Mach trim. I turned on autopilot to see if the autopilot could trim it out. That resulted in a autopilot Nose Up Trim Caution message and I turned off the autopilot and resumed manually flying the aircraft. The nose up trim condition did not improve. I transferred aircraft control to the First Officer while I referenced the QRH. I read through the stab trim and Mach trim runaway procedures even though we did not get a runaway trim message. Every time we tried to reset stab/Mach trim the trim increased by .4 and would not let us lower the trim value making the aircraft more nose up trimmed. I advised ZZZ Departure and ran the appropriate check lists and returned to the field landing on Runway 28L.I think the main problem was the Mach trim inputs from the aircraft computer system which caused the stab trim indicator to increase every time we disconnected and re engaged the stab/Mach trim system. The pilots went back to the hotel after the flight. I ran into the pilots who bought the aircraft in the night before at the hotel and they said that they had an autopilot nose up trim situation after take off from ZZZ1 and they reset it according to the QRH with no other problems.
Captain reported an uncontrollable Mach Trim condition that caused an Air Turn Back and precautionary emergency landing.