As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING POST FLIGHT INSP WITH THE APU RUNNING AND BLEED AIR SELECTED ON, IT WAS NOTED THAT THERE WAS A HOLE IN THE INSULATION OF THE APU AND GROUND START DUCT, AND BLEED AIR FELT TO BE ESCAPING. FURTHER INVESTIGATION FOUND THAT A TWO (2) INCH CRACK HAD DEVELOPED IN THE WELDED SEAM AT THE "Y" SECTION OF THE APU AND GROUND START DUCT.