What was found
ON FLIGHT 4099 THE CREW REPORT THAT DURING CRUISE AT FLIGHT LEVEL 290 THE AIRCRAFT YAWED RIGHT, NOTED THAT ENGINE 2 N1 TARGET AND N1 INDICATION DECREASING TO LESS THAN 70% WITHOUT TL MOVEMENT N1 DECREASE TO APPROXIMATELY 87.5% WITH SLIGHT VARIATION FOR APPROXIMATELY 5 MINUTES. THE AIRCRAFT YAWED RIGHT A SECOND TIME N1 TARGET AND N1 ON ENGINE 2 DROPPED TO THE LOW 60% RANGE AND RECOVERED TO APPROXIMATELY 87.5%. NO POWER VARIATION NOTED ON DESCENT OR LANDING. ON ROLL OUT AFTER LANDING NO MESSAGES APPEARED ON EICAS FOR ENGINES 1 AND 2. THE AIRCRAFT LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. REMOVED AND REPLACED THE FULL AUTHORITY DIGITAL ENGNE CONTROL 2B (FADEC). THE AIRCRAFT WAS RETURNED TO SERVICE.