As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PRIOR TO ENGINE START, GROUND PERSONNEL NOTICED A FLAME IN THE RIGHT WHEEL WELL AND APU EXHAUST DUCT AREA. THE APU WAS SHUTDOWN USING A FIRE SWITCH AND FLAMES EXTINGUISHED. MAINTENANCE REPLACED THE APU FIRE EXTINGUISHER BOTTLE, CLEANED THE WHEEL WELL AREA AND INSPECTED THE AREA FOR DAMAGE. NO DAMAGE NOTED THE APU WAS PLACED ON MEL.