What was found
AT THE GATE, APU FAULT MESSAGE APPEARED, APU AUTO SHUTDOWN OCCURRED. ALSO, BEFORE SHUTSDOWN OCCURRED, COULD DETECT ELECTRICAL BURNING ODOR THROUGHOUT CABIN WITH PACKS ON APU AIR. INSPECTED APU, NO NOTICEABLE BURNS NOTED. REMOVED AND REPLACED APU, S/N P-626, REMOVED OFF MEL. FINDINGS REVEALED THAT PRIMARY FAILURE WAS THE SEPARATION OF THE COMPRESSOR IMPELLER. STARTER CHARRED. (M)