As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD INFLIGHT T1861/13APR - CREW REPORTED SMELL OF BURNING DEICING FLUID IN AIR CONDITION SYSTEM. CABIN FILLED WITH SMOKE. CREW SHUT DOWN RIGHT PACK. RETURNED TO ORD AND LANDED WITHOUT INCIDENT. FOUND APU HAD INGESTED FLUID. REPLACED AUXILIARY POWER UNIT AND ACCOMPLISHED BURNOUT OF HIGH PRESSURE PNEUMATIC DUCTING. SYSTEM GROUND CHECKED NORMAL OPERATION.