As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAILED IN FLIGHT, THE APU FAULT LIGHT AND EICAS ILLUMINATED. PERFORMED AN APU BITE TEST IAW MM 49-61-05-742-049. REVERSE FLOW PRESENT ON BITE. IAW FIM 49-11-00-815-880-002-2. REMOVED AND REPLACED THE APU SURGE VALVE IAW MM 49-53-01. OPS CHECKED GOOD, NO FAULTS SHOWN ON APU BITE CHECK.