Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 25; Flight Crew Total 3650; Flight Crew Type 1200
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem
Aircraft
During cruise at FL410 there was an uncommanded disconnect of the Automatic Flight Control System (AFCS). Loss of Autopilot (AP); Yaw Dampener (YD); and Auto Throttles (AT). Dutch Roll developed becoming divergent. Attempts were made to reengage the YD. Switching AFCS channels initially unsuccessful. As the Dutch Roll was increasing in amplitude; continued manual flight was proving difficult. Crew elected to initiate immediate descent to FL370 and inform ATC. AFCS restored as aircraft descended out of FL410. Descent continued to FL370. Operations normal; QRH consulted - continued flight on one remaining AFCS channel.
Global 5000 (Bombardier) Captain reported a malfunction of the Automatic Flight Control System; which resulted in uncontrollable Dutch Roll until arriving at a lower altitude.