Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition
Aircraft
In cruise at FL300; with a previous malfunction causing the loss of hydraulic system 3; the aircraft had a FCC [Flight Control Computer] 2b and a DEU [Display Electronic Unit] #2 failure. The failures caused the autopilot to disengage; the throttles to retard to idle and the airspeed envelope to close causing an over speed warning. Pilot Flying immediately lowered the nose and advanced the throttles to prevent a stall condition. Aircraft lost approximately 1;000 feet prior to the pilot returning aircraft to its assigned altitude. Notified ATC of the situation and ran appropriate checklist to recover systems. We then requested clearance to return to ZZZ. On return; we [advised ATC] and dumped approximately 65;000 lbs. of [fuel] to bring aircraft below maximum landing weight. Captain made an uneventful landing to Runway XXR; we then proceeded to taxi aircraft to the [Company] ramp. Loss of multiple systems; FCC 2b; DEU (Display Electronic Unit) #2; Hyd (Hydraulic) #3 with multiple secondary alerts.
Air carrier pilot reported loss of multiple systems while in cruise.  Flight crew advised ATC and returned to departure airport.