As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PIT- FLT 4153 - CRWE REPORTED WITH APU RUNNING AND MAINTEANCE ON BOARD THE CABIN AND COCKPIT FILLED WITH SMOKE. CREW SAID IT SEEMED TO BE COMING FROM THE NR 2 PACK. MAINTENANCE RAN THE NR 2 PACK WITH THE APU AND FOUND NO ODOR. SUSPECT ANTI-ICE FLUID ENTERED THE APU BLEED SYSTEM. COULD NOT DUPLICATE DISCREPANCY AND AIRCRAFT WAS RETURNED TO SERVICE. (M)