What was found
DURING CRUISE AT 40,000 FEET, AUTOPILOT FAIL, YAW DAMPER FAIL AND VENTRAL RUDDER FAIL CAS MESSAGES ALL DISPLAYED AT THE SAME TIME. ACFT IMMEDIATELY STARTED TO DUTCH ROLL, A EMERGENCY DECENT WAS STARTED AND AT THIS TIME THE DUTCH ROLL WAS EXCEEDING 30 DEGREES TO BOTH SIDES, IT APPEARED TO STAY THIS WAY UNTIL THE ACFT WAS APPROXIMATELY 25,000 FT, ABLE TO REGAIN THE YAW DAMPER, KEPT DECENT GOING TO 10,000, AND LEVELED OFF. LANDED WITHOUT FURTHER PROBLEMS. REPLACED AND CONFIGURED ROLL SERVO REFERENCING TASKS AMM 22-11-02-000-801A, 22-11-02-400-801A AND 22-11-02-470-801A . OPS TESTED SATISFACTORY. REPLACED AND CONFIGURED VENTRAL RUDDER SERVO REFERENCING TASKS AMM 22-11-11-000-801A, 22-11-11-400-801A AND 22-11-11-470-801A. OPS TESTED SATISFACTORY.