As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER APU START STRONG BURNING ODOR IN COCKPIT. APU BLEED CLOSED PACKS WERE OFF VISUAL INSPECTION SHOWED SMOKE COMING OUT OF APU AIR INLET & EXHAUST. TROUBLESHOT BURNING SMELL TO RESIDUAL DE-ICE FLUID IN THE APU AREA. NO DEFECTS OR SMELL NOTED, CLEANED RESIDUAL FLUID.