What was found
UN-COMMANDED RAPID ROLLBACK OF BOTH ENGS TO THE IDLE POSITION, OCCURRED DURING CRUISE FLIGHT. THE AUTO THROTTLE ARM SWITCH WAS ON. THE ENG & WING ANTI-ICE SWITCHES WERE IN AUTO. THE THRUST LEVERS FOLLOWED ENGS TO IDLE POSITION. THE CREW THEN DISCONNECTED THE AUTO THROTTLES & TURNED THE ENG ANTI-ICE SWITCH TO ON. COMPLIED WITH THE ENG LIMIT OR SURGE OR STALL CHECKLIST. RESTORED NORMAL THRUST, RECONFIGURED SWITCH POSITIONS TO NORMAL & THE ENGS CONTINUED TO OPERATE WITH NO FURTHER ABNORMALITIES. ACCOMPLISHED MAINTENANCE CONTROL DISPLAY PANEL TESTS 52, 57 & 60 IAW FIM 22-04-FAULT TREE 802. NO CAUSE OF UN-COMMANDED ROLLBACK OF BOTH ENGS WAS FOUND.