What was found
SMOKE ODOR IN CABIN DURING FLIGHT, NEAR ROW 34. INITIALLY DISSIPATED & RETURNED STRONGER. CREW REPORTED BURN RUBBER SMELL BETWEEN ROWS 29-34. PAX & CREW TRIED PIN POINT ODOR & COULD NOT LOCATE. TECHOPS AND FIRE DEPART. PERFORMED A VISUAL & SMELL INSP OF CABIN & COULD NOT LOCATED SOURCE IAW FIM TASK 21-00, TASK 830. INSPECTED RECIRCULATION AIR FILTERS. FOUND RECIRP FILTERS DIRTY. R & R RECIRC AIR FILTERS AS A PRECAUTION IAW AMM 21-25-01-000-801. ON FIM TASK 21-00 TASK 830 COMPLETED TEST PARAGRAPH -J- RAN BOTH ENGINES & COMPLETED TEST FOR OIL FUMES PARAGRAPH -N- & ELECTRICAL FAULTS PARAGRAPH -Q-. FOUND NO BURNING ODOR BETWEEN ROWS 29 & AFT CABIN.