As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH - FLT 0126 - THE APU AUTO SHUT-DOWN DURING CLIMB-OUT AT 27,000 FEET. APU RESTART WAS UNSUCCESSFUL. THE AIRCRAFT WAS RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND APU LOAD CONTROL VALVE PARTIALLY OPEN DURING START AND UNDER NO LOAD. WHEN LOAD WAS APPLIED, APU FREQUENCY WOULD DROP OFF LINE. THE LOAD CONTROL VALVE WAS REMOVED AND REPLACED AND OPERATION CHECKED GOOD. )X)