As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER CONDUCTING 133D HOIST OFFSHORE AT NIGHT. WHILE ENROUTE NR 1 ECU, ENGINE CONTROL UNIT, FAIL WARNING LIGHT ILLUMINATED. NR 1 ENGINE REVERTED TO MANUAL MODE. PILOT SET GOVERNOR CONTROL SWITCH TO MANUAL, AND TRIMMED THE ENGINE BELOW THE NR 1 ENGINE. MANUALLY CONTROLLED ENGINE TO LANDING AT DEPARTURE AIRPORT. UNABLE TO DUPLICATE PROBLEM AFTER ENGINE RESTART. STILL TROUBLESHOOTING.