What was found
DESCENDING THROUGH 16K ON APPROACH, A BURNING SMELL NOTICED BEGINNING AT ROW 34RT. SMELL SPREAD THROUGHOUT CABIN AND WAS SIMILAR TO BURNING POPCORN. F/A'S CKD FLOOR AT ROW 34 AND REPORTED FLOOR WAS WARM. SMELL DISSIPATED ON LANDING AFTER A/C WAS DEPRESSURIZED. NO VISIBLE SMOKE NOTED. FOUND APU AIR DUCT AT STA 1300 IN AFT BAG BIN CRACKED. REPLACED DUCT.