What was found
DURING TAXI OUT MAIN DECK CARGO SMOKE DETECTOR "B" LOOP INDICATED SMOKE. ECAM INDICATED SMOKE IN AFT COMPARTMENT. STOPPED AIRCRAFT AND COMPLIED WITH ECAM. WARNING EXTINGUISHED WHEN NR 2 PACK VALVE TURNED OFF. RETURNED TO GATE. MAIN DECK CARGO DETECTOR AFT LOOP A INOP-PREV-MEL. AFTER BLOCK IN FOUND APU LEAKING OIL INTO APU INTAKE CAUSING SMOKE IN CABIN DURING PACK OPERATION. REMOVED AND REPLACED NR 1 AND 2 PACK COALESCER BAGS, REF MM 21-51-16-3. MEL'D APU SEE WRI 49-10/0023. RAN ENGINES AT POWER TO CLEAR PNEUMATIC DUCTS OF OIL RESIDUE PER MM 21-51-00-3. NOW BOTH AIR-CONDITIONING PACKS WORK AND SMELL NORMAL.