What was found
STRONG ODOR CIRCULATED THROUGHOUT ENTIRE AIRCRAFT DURING DESCENT FROM FL200 DOWN TO THE SURFACE, SMELLED LIKE DIRTY SOCKS & CHEMICALS. NOTICED SMELL IN CABIN UPON ENTRY TO AIRCRAFT. ISOLATED EACH BLEED SYSTEM AND OPERATED PACKS ON FULL HOT/ FULL COLD. SMELL DISSIPATED WHEN OPERATING PACKS WITH NR 1 ENGINE BLEED. MONITORED OIL QTYS OF ENGINES AND APU BEFORE DURING AND AFTER ENG RUN. QTYS NORMAL. OPENED NR 1 ENGINE TR COWL AND VISUALLY INSPECTED #1 ENG EXTERNALLY, NO LEAKS NOTED. SUSPECT SMELL WAS FROM RESIDUAL OIL PRIOR TO NR 1 ENG CHANGE. REFERENCE TSM 05-50-00, AMM 71-00-00 & AMM 21-51-00. OK FOR SERVICE.