As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON INITIAL WALK AROUND SPARKS WERE SEEN COMING OUT OF THE EXHAUST BEFORE APU SHUT DOWN. ACCOMPLISHED BORESCOPE FOUND DAMAGE TO BE BEYOND ALLOWABLE LIMITS. REMOVED AND REPLACED APU IAW ATI TASK CARD JC-49-999-00-01. ALL OPERATIONAL AND LEAK CHECKS GOOD.