What was found
PASSING 8000 FEET ON CLIMB OUT, PASSENGER AND CREW DETECTED AN ODOR ORIGINATING IN THE AREA OF ROW 4, ODOR WAS NOTICED FROM FLIGHT DECK TO ROW 20. AIRCRAFT RETURNED FOR INSPECTION. ODOR DECREASED AFTER LANDING. LANDING WEIGHT 138,000 LBS. PERFORMED TASK 24-00-00-810-823 AND TASK 23-39-810-801. NO DEFECTS NOTED. REPLACED RECIRCULATION FILTER PRECAUTIONARY IAW AMM 21-21-41. NO OTHER DEFECTS NOTED AIRCRAFT OK FOR SERVICE. (K)