What was found
BOS - FLT 153 - EN ROUTE BOS-ORD AT GATE, SHORTLY BEFORE DEPARTURE DETECTED HEAVY SMOKE AND HAZE IN CABIN AND COCKPIT. REPLACED BOTH PACK FILTERS. ACCOMPLISHED PACK BURNOUT, RAN BOTH ENGINES, AND APU PER THE MM. NO SMOKE OR HAZE NOTED. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)