As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: DURING APU START, THE APU SHUT DOWN ALL ELECTRICITY AND AIR. BATTERY WAS DISCHARDING AND RAMP PERSONNEL NOTED FLAMES COMING FROM OUTSIDE THE APU TAIL PIPE AREA. FLAMES WRAPPED AROUND EXHAUST AND FLAMES EXTINGUISHED, NO FIRE EXTINGUISHING AGENT WAS USED. MAINTENANCE REMOVED AND REPLACED APU IAW CARD 49-94-11. OPS CHECK NORMAL. LEAK CHECK OKAY.