What was found
BOS - FLT 1055 - AFTER TAKEOFF, A BURNING SMELL OF OIL AND SMOKE WERE NOTED IN THE CABIN. AIRCRAFT AIR INTERRUPTED AND RETURNED TO BOS WITHOUT FURTHER INCIDENT. REPLACED APU OIL FILLER CAP AND AS A PRECAUTIONARY, REPLACED BOTH COALESCER BAGS. SYSTEM GROUND AND LEAK CHECKED, NORMAL OPERATION. (X)