ACFT AUTOPLT HAS TRIM RUNAWAY AND RESULTS IN SHARP NOSE UP GAINING 3000 FT OF ALT.

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ON THE LEVELOFF AT 5000 FT MSL (ASSIGNED); WE HAD AN AUTOPLT TRIM RUNAWAY. THE ACFT VIOLENTLY PITCHED UP AND CLBED APPROX 3000 FT BEFORE WE REGAINED CTL OF THE ACFT. DISABLING THE AUTOPLT CIRCUIT BREAKER SOLVED THE PROB. WE ADVISED ATC OF THE PROB AND RETURNED TO CMH WITHOUT INCIDENT. SUPPLEMENTAL INFO FROM ACN 327579: AT THE INITIAL LEVELOFF; MY COPLT WAS HAVING A PROB MAINTAINING 5000 FT MSL. HE WAS ATTEMPTING TO ENGAGE THE AUTOPLT (ALT HOLD). I ASSUMED THAT HE WAS ONLY TRYING TO TRIM THE ACFT. THE AUTOPLT FAIL LIGHT WAS FLICKERING AND I NOTICED THE TRIM WAS ROLLING NOSE UP; TAKING US FURTHER OFF OUR ALT. HE SAID; 'WE HAVE A PROB.' I SAW HE WAS FIGHTING WITH THE YOKE. THE TRIM CONTINUED TO ROLL THE ACFT NOSE UP. I PUSHED THE TRIM DISCONNECT ON MY YOKE AND THE TRIM CONTINUED TO ROLL. I TURNED THE TRIM OFF ON THE PEDESTAL AND THE TRIM WAS STILL ROLLING. I TOLD HIM TO GIVE ME THE ACFT CTLS SO THAT HE COULD PULL THE ELEVATOR TRIM CIRCUIT BREAKER. HE GAVE ME THE CTLS; AND I REALIZED WE HAD A SERIOUS PROB. I COULDN'T HOLD ENOUGH FORCE ON THE CTLS TO HOLD ALT. HE PULLED THE BREAKER AND THE ACFT WAS STILL CLBING WITH BOTH OF US USING AMAZING FORWARD PRESSURE ON THE CTLS. I ALERTED ATC THAT WE NEEDED TO DIVERT TO CMH AND THAT WE WERE HAVING A TRIM RUNAWAY. WE TURNED THE AUTOPLT OFF AND ON WITH THE AUTOPLT CTLR AND IT FINALLY STOPPED MOVING. BEING UNABLE TO MOVE THE MANUAL TRIM WHEEL BEFORE; WE WERE NOW ABLE TO TRIM THE ACFT MANUALLY BACK TO LEVEL FLT. WE GAINED 3000 FT IN THE OCCURRENCE. WE FOUND OUT ON THE GND THAT THE AUTOPLT TRIM HAD FAILED AND THAT CTL FORCES COULDN'T OVERRIDE THE AUTOPLT SYS. WE WERE AWARE OF THE FACT THAT OUR NEXT STEP WOULD HAVE BEEN TO SHUT DOWN THE AVIONICS OR PULL THE AVIONICS MASTER CIRCUIT BREAKER. THE TIME FRAME FROM START TO FINISH WAS PROBABLY 1-2 MINS.