What was found
FLT#2136, PHX-JFK. 'MAGIC MARKER FUME EVENT ON DESCENT 11K TO GROUND BOTH BACKS. ISOLATING THE PACK DID NOT HELP.; COMPLIED WITH INFO NOTICE 2017-TO15 NO ODOR NOTICED ON ENGINES, DETERMINED APU TO BE AT FAULT SO PLACED APU ON MEL . PERFORMED LEVEL B PACKS DECONTAMINATION REF AMM 21-00-00. REF LOG PAGE 3447813 ITEM #1 (REMOVED AND REPLACED CABIN RECIRCULATING FILTERS IAW AMM 21-21-41 . A/C OK FOR SERVICE. ) FOR REMOVAL AND REPLACEMENT OF RECIRCULATING FILTERS.'