What was found
ORD - FLT 0447 - AFTER TAKEOFF, FLIGHT CREW SMELLED AND SAW SMOKE IN COCKPIT. FLIGHT ATTENDANT CONFIRMED THE SAME IN THE FORWARD CABIN. AIRCRAFT RETURNED TO ORD AND LANDED WITHOUT INCIDENT. MAINTENANCE CLEANED APU AND FOUND A LOOSE B-NUT AT TEE FITTING. TIGHTENED B-NUT AT TEE FITTING WITH NO FURTHER LEAK NOTED. RAN PACKS AND ACCOMPLISHED BURN-OUT WITH NO SMOKE NOTED. SYSTEM GROUND CHECKED, NORMAL OPERATION. (X)