What was found
FLT # 1807, BOS-BNA. ON DEPARTURE CLM SFC-5000 CABIN ODOR DETECTED BY COCKPIT CREW/ FWD FA IN CABIN THEN DISSIPATED IN CLM. ON DESCENT BELOW 4000 ODOR RETURNED ODOR DESCRIPTION TO BE MUSTY ( DIRTY SOCK) MODERATE-INTENSITY APPROX 5 MIN DURATION COCKPIT FWD CABIN AIR SUPPLY VENT SUSPECT NO APU BLEED AIR SUSPECT. ( PACKS ) ; PERFORMED DECONTAMINATION OF PACK 1 AND PACK 2 IAW AMM 21-00-00. NO SMELL NOTED AT THIS TIME. MX-4 UPDATED AND PLACARD REMOVED.