What was found
F/A'S REPORT "DIRTY SOCK" SMELL IN CABIN ON T/O DEPT, AND THEN AGAIN ON APPROACH/LANDING. GROUNDED - YES. OPERATED BOTH PACKS ON HIGH WITH APU, NO SIGN OF ODOR DETECTED. BLACK LIGHT TEST OF SWABS FROM APU LOAD COMPRESSOR WITNESS DRAIN WERE INCONCLUSIVE. ENGINEERING REQUESTS ADDITIONAL INVESTIGATION OF APU AS POSSIBLE SOURCE OF ODOR. REMOVED AND REPLACED APU REF AMM 49-11-00. ACCOMPLISHED APU INSTALLATION AND OPERATIONAL TESTS REF AMM 49-11-00. NO LEAKS NOTED. OPS CHECK NORMAL. ACCOMPLISHED APU BITE PROCEDURE REF AMM 49-61-00. NO FAULTS FOUND.