As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, CREW NOTED LT ENGINE ROLL BACK FROM 95.7 TO 91.0 WITH SIMULTANEOUS FUEL FLOW AND ITT FLUX. AC WAS AT FL 380 WITH AN OAT OF -33 C IN CLEAR AIR. ENGINE ANTI-ICE WAS OFF. MAINTENANCE FOUND THE LEFT HMU FAILED. IT WAS REPLACED