What was found
ORD - FLT 1631 - ODOR IN CABIN BOTH ON GROUND AND IN AIR. AFTER TAKEOFF, ODOR WAS STRONGER AND A SMOKY APPEARANCE WAS NOTED THROUGHOUT CABIN. LANDED ORD WITHOUT INCIDENT. REPLACED APU OIL COOLER SUPPLY LINE O-RING. ACCOMPLISHED BURN OUT OF HIGH PRESSURE PNEUMATIC DUCTING PER MM. REPLACED COALESCER BAGS. NO SMOKE NOTED. SYSTEM GROUND CHECKED, NORMAL OPERATION. (X)