As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER PASSING THROUGH FL 360, APU QUIT WITH FAULT LIGHT AND WOULD NOT RESTART SINGLE GENERATOR. OPS ON RETURN TO ATL DUE TO LEFT ENG GENERATOR INOP ON MCO AND PLACARD. SERVICED APU OIL TO FULL. ECU BITE SHOWED OVERSPEED FOR AUTO SHUTDOWN. T/S PER FIM 49-11-00 FIG 111. REMOVED AND REPLACED FCU PER M/M. APU CHECKS GOOD.