As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
COCKPIT FILLED WITH SMOKE RAPIDLY 10 MINUTES AFTER APU STARTED UP FOLLOW BY BURNING SMELL. WE SHUT DOWN THE ACFT RIGHT AWAY. ALSO SMOKE IN THE MAIN CABIN. UNABLE TO DETERMINE WHERE THE SMOKE IS COMING FROM. COMPLIED WITH AIR CYCLE MACHINE REPLACEMENT IAW CMP 215012. OPERATIONS TEST WAS GOOD.