As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO FIELD AFTER THE NR 1 ENGINE SURGED. ECM SHOWS NO RECORD OF A SURGE/STALL. EEC/FADEC RECORDED NO STALL MESSAGE. FMU WAS REPLACED FOR N1 OVER SPEED AND CHANNEL B FAULT. FMU TEST SHOWS NO FAULT FOUND. CAUSE OF SURGE CAN NOT BE DETERMINED.