What was found
CREW REPORTED, AT CRUISE ALTITUDE, ACFT BEGAN ENCOUNTERING ICING CONDITIONS. WING AND STABILIZER DEICE BOOTS FAILED TO REMOVE ICE. CREW REPORTED SURFACE DEICE SYS AS INOPERATIVE ALTHOUGH SYS HAD CHECKED NORMAL EARLIER IN THE DAY. SEVERAL ATTEMPTS AT CHANGING ALTITUDE TO GET CLEAR OF ICING CONDITIONS FAILED. CREW REQUESTED DIVERSION, WHERE CONDITIONS WERE REPORTED TO BE BETTER. ON DESCENT, SURFACE DEICE SYS BEGAN WORKING AND ICE WAS SHED FROM WINGS AND STABILIZERS. CONTINUED APPROACH AND LANDED WITHOUT INCIDENT. MX INSPECTED SURFACE DEICE SYS, AND PERFORMED SEVERAL SYS CHECKS, BUT COULD NOT DUPLICATE FAILURE. AS A PRECAUTIONARY MEASURE, MX R & R RT STUB WING BOOT (SEVERAL PATCHES), VERTICAL STABILIZER BOOT (SEVERAL PATCHES), SURFACE DEICE SWITCH AND DEICE TIMER.