As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON PRE-FLIGHT WITH APU RUNNING SMOKE ENTERED FLIGHT DECK AND ALL AIR CONDITIONING DUCTS. SPARKS WERE SEEN EXITING APU EXHAUST AREA. APU FIRE HANDLE WAS PULLED AND BOTH FIRE BOTTLES WERE DISCHARGED. INSTALLED APU PER W/C 49T1901, APU OPS CHECKED GOOD WITH NO DEFECTS AT THIS TIME.