As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE USING APU TO POWER AIRCRAFT, AIRCRAFT STARTED TO FILL WITH SMOKE. APU MADE SEVERAL LOUD BANGS, APU WAS SHUT DOWN. SMOKE CONTINUED FROM EXHAUST. *S/D* FRONT COMPRESSOR BEARING FAILED. COMPRESSOR IMPELLER RUBBED HOUSING, FRONT SEAL DESTROYED CAUSING CONDITION. METAL WAS FOUND IN GEARBOX FILTER SCREEN.