What was found
ACFT ON GROUND RUNNING APU FOR ABOUT 3 HOURS BEFORE DEPARTURE. ON TAKEOFF, SMALL AMOUNT OF SMOKE IN CABIN AND COCKPIT. RETURNED TO AIRPORT AND LANDED. PERFORMED AN INSP OF APU AREA AND FOUND SMALL AMOUNT OF OIL IN AREA. PERFORMED GROUND POWER ENGINE RUNS AND NO SMOKE NOTED. PERFORMED OPS FLIGHT TO CHECK SYS. SYSTEM CHECKED OK. NO SMOKE NOTED. (K)