As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INVESTIGATION FOR A DOUBLE INVERTER FAILURE FOUND OPTIC COUPLER IN PHASE LOCK CIRCUIT FALIED. WITH COUPLER FAILED FREQ OUTPUT UNREGULATED, CAUSING PHASE LINK TO DISCONNECT THE OTHER INVERTER. PHASE LINK NOT PROTECTED BY FAULT MONITOR AND CAN FAIL BOTH INVERTERS. SUBMITTER SUGGESTS REDESIGN FAULT CKT TO PROTECT UNIT FROM DUAL FAILURE.