As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU BLEED PREASURE WAS 4 PSI ON ENGINE START. ACFT RETURNED TO GATE. COULD HEAR BLEED AIR LEAK ON THE NR 2 ENGINE COWL. GAINED ACCESS FOUND MAIN SUPPLY DUCT CLAMP TOP OF ENGINE BLOWN OFF , PIPE CONNECTION SEPORATED WITH SEVERAL WIRE BUNDLES NEAR IT MELTED. NR 2 ENGINE CHANGED.