As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU BLEED AIR: THE COCKPIT FILLED UP WITH SMOKE AFTER THE APU BLEED AIR WAS TURNED ON. // SIGNOFF // PERFORMED BORESCOPE INSPECTION OF THE APU COMPRESSOR, NO SIGN OF OIL WAS NOTED REF SQUAWK 2.4 OF THIS WORK ORDER FOR FURTHER DETAILS ON WORK ACCOMPLISHED. (COMPLY WITH TASK CARD TC-68A-21-18 I 006M ENVIRONMENTAL CONTROL SYSTEM BLEED DUCT BURN PROCEDURE REMOVED AND REPLACED HEPA FILTER WITH A "NEW" UNIT IAW CE-680A MM 21-70-10