What was found
AT FRA, A/P WOULD NOT ENGAGE AND THE MESSAGE AP FAIL APPEARED. RESET AND ENGAGED THE AUTOPILOT TWICE, BUT IT FAILED IMMEDIATELY BOTH TIMES. THE AIRPLANE KEPT PITCHING UP AGGRESSIVELY, SO, MOVED THE TRIM ALL THE WAY FORWARD MANUALLY, BUT THAT DIDN’T HELP. REDUCED THE POWER AND THE AIRPLANE STARTED TO PITCH DOWN AGGRESSIVELY.BOTH PILOTS HAD TO HOLD THE YOKE IN ORDER TO MAINTAIN CONTROL AND OVERCOME THE FORCES. EVENTUALLY, WAS ABLE TO MAINTAIN SOME CONTROL BY ADJUSTING THE POWER ENOUGH TO MAINTAIN ALTITUDE AND ATTITUDE.