What was found
FLT 1907, BOS-BNA. ON DESCENT AROUND 12000 FT STRONG DIRTY SOCK SMELL (CAT LITTER SMELL) WAS IN COCKPIT. UPON ARRIVAL ALL 4 F/A'S COMPLAINED ALSO ABOUT SMELL. COCKPIT, FWD AND AFT GALLEYS AFFECTED; C/W INFO NOTICE 2017-T015D SECTION A. ISOLATED TO APU BLEED AS SUSPECT SOURCE. SEE ITEM 2 FOR APU BLEED MEL A/C OK FOR SERVICE. NOTIFIED MCC. PERFORMED INSP. OF APU AREA, INTAKE, AND EXHAUST PER TSM 49-00-81, NO CONTAMINATION NOTED. PERFORMED OPS TEST REF AMM 12-33-21, NO ODOR PRESENT. MDDR CLEARED, MX-4 UPDATED, PLACARD REMOVED.