What was found
ORD - FLT 0878 - EN ROUTE, SJC/ORD SHORTLY AFTER TAKEOFF, A BURNING ODOR WAS NOTICED THROUGHOUT CABIN. FLIGHT ATTENDANTS THEN REPORTED VERY LITTLE AIR FLOW COMING THROUGH AIR VENTS AND GASPERS FOR DURATION OF FLIGHT. LANDED ORD WITHOUT INCIDENT. INSPECTED LEFT AND RIGHT PACK SYSTEMS WITH BOTH ENGINES AT ALL POWER SETTINGS. FLOW CHECKED NORMAL, NO FOUL ODOR NOTICED. RE-ATTACHED BLOWN DUCT CAP IN OVER HEAD SUPPLY DUCT. REPLACED LEFT RECALCULATION AIR FILTER, SYSTEM GROUND CHECKED, NORMAL OPERATION. (X)