What was found
CREW REPORTED ON CLIMB OUT WITH AUTOPILOT ON THE AMBER ICAS, STAB TRIM + MACH TRIM POSTED. FOLLOWED CHECKLIST & CHANNEL 1 & 2 WOULD NOT ENGAGE. CHECKED ALL CB’S & ALL IN. CYCLED THE PILOTS & COPILOTS PITCH TRIM YOKE DISCONNECTS NO CHANGE. CONTINUED FLIGHT WITH PITCH TRIM FAILED. PRIOR TO LANDING TRIED TO RESET AGAIN & NO CHANGE. CHANNEL 1 & 2 STILL WOULD NOT ENGAGE. ON APPROACH CREW REPORTED THEY HAD EXCESSIVE NOSE DOWN & BOTH PILOTS HAD TO HOLD THE YOKE BACK. POWERED DOWN PLANE & WHEN POWERED BACK UP PROBLEM WAS GONE & PITCH TRIM WORKED NORMALLY. MX FOUND THAT IF THEY ROCKED THE COPILOTS DISCONNECT SWITCH THEY COULD DUPLICATE THE FAILURE. CONFIRMED THAT WHEN IT FAILED HSTECU LABEL 270 BIT 14 SET FOR APPROX 2 MINUTES.