MD-80 Series (DC-9-80) Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; Flight Crew Diverted; General Maintenance Action
Aircraft
After takeoff on climb out aircraft seemed to be in a slight slip/ out of trim not too unusual for this fleet; I was hand flying with use of Flight Director in:  EPR LIM; HDG SEL; ALT set for 15000; and IAS 250 knots. As we passed through 10;000 feet I inputted rudder trim [and] we heard/felt a pop as if something broke. The aircraft then began rolling left and right due to rudder yaw - it was as if we were in a Dutch roll scenario. I immediately slowed the ascent rate. We then requested a return to [departure airport]. Notified ATC of our predicament; started a slow descent toward [departure airport]. All control inputs after this point were small; smooth and measured in an attempt to gather information as to what we may anticipate the aircraft state may be in the future as we prepared for approach and landing. When aircraft was slowed and configured for approach and landing the aircraft flight controls seemed to become more effective. A visual approach and landing was completed in normal fashion. Weather was VFR; winds at 210/13kts.
At approximately 10;000 feet and 250kts; the Captain began trimming the rudder while hand flying. It immediately felt like something broke in the flight controls and the aircraft began to shake; roll and yaw fairly violently. We then got a Yaw Damper and Mach Trim caution light. We landed without incident with Aircraft Rescue and Firefighting (ARFF) on standby. ARFF checked the exterior of the aircraft and cleared us to taxi to the gate. Upon reaching the gate; we found Circuit breaker C18; DFGC (Digital Flight Guidance Computer) System popped.
MD-80 flight crew reported returning to departure airport after experiencing a rudder flight control anomaly.