As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE FLYING AT FL410, N1 SPEED ON BOTH ENGINES WAS SET AT 92, 5 PERCENT WITH SYNC ON WHEN THE RT SUDDENLY CAME DOWN TO 84-85 PERCENT AND FLUCTUATING FOR APPROXIMATELY 5 MIN. THE ACFT LANDED SAFELY AND TROUBLESHOOTING IS ON-GOING, FOLLOWING FAULT CODES FOUND ON THE ENGINE DOWNLOADS.