As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING PUSH BACK AND ENGINE START OF RIGHT HAND ENGINE, AUXILIARY POWER UNIT FAULT LIGHT AND SHUTDOWN. AUXILIARY POWER UNIT HAD INTERNAL SEIZURE, CAUSING TURBINE TO BE DISCHARGED. METAL PIECE WAS EJECTED OUT OF EXHAUST PORT. AUXILIARY POWER UNIT CHANGED AND OPERATION CHECK CARRIED OUT. FURTHER INFORMATION WILL FOLLOW AFTER INVESTIGATION.