As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX INFLIGHT - DURING APPROACH WITH TAIL DE-ICE SELECTED CREW REPORTED STRONG BURNING SMELL WITH SOME OBSTRUCTED VISIBILITY DUE TO SMOKY AIR. LANDED PDX WITHOUT INCIDENT. INSPECTED ENGINES, APU, AIR CONDITIONING PACKS AND SURROUNDING AREAS FOR LEAKS AND DISCREPANCIES. NO DISCREPANCIES NOTED. ACCOMPLISHED PACK BURN ON BOTH PACKS AND DUCTING. SYSTEM GROUND CHECKED NORMAL OPERATION.