As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING ENGINE NR 2 START LOSS OF ELECTRICAL, SWITCHED GENERATOR TO ENGINE NR 2. APU EMITTED SMOKE AND FLAME, APU EGT AT 918C. SHUTDOWN APU IMMEDIATELY, STRONG BURNING SMELL IN COCKPIT. EMERGENCY DECLARED, A/C RETURNED TO GATE. TRANSFERRED APU TO DEFERRED LIST PER MEL 49-10-01-1.