What was found
AT FL 350, DURING CRUISE, APPROXIMATELY 42 MIN INTO FLIGHT, A DISTINCT ODOR PERSISTED WHILE IN CRUISE, SMELLED LIKE DIRTY LAUNDRY. STRONG IN COCKPIT. CABIN REPORTED NO ODOR. ACCOMPLISHED TSM 05-50-00-810-831-A. RAN APU AND ENGINES AND PACKS. ENGINES AT HIGH POWER AND IDLE, NO DISCREPENCIES FOUND. REPLACED RECIRCULATION FILTERS WHICH WERE FOUND SOMEWHAT DIRTY FOR PRECAUTIONARY PURPOSES. A/C OK FOR SERVICE.