As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU SHUTDOWN AT GATE (2ND TIME). APU INOP, OK TO DEFER IAW MEL. NOTIFIED OPB & DD. APU STARTED NORMALLY. ALL APU PARAMETERS STABILIZED OK WITH HIGH LOADS IMPOSED FOR 20 MIN. NO APU SHUTDOWN OCCURED. FLEXIBLE DUCT FOUND BROKEN. REPLACED DUCT AND APU START NORMAL