As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU RED FIRE CAS ILLUMINATED IN FLIGHT. AIRCRAFT LANDED WITHOUT INCIDENT. INSPECTED APU FIRE LOOP ASSEMBLY AND EXHAUST SHIELD WITH NO EVIDENCE OF FIRE. APU FIRE WARNING INDICATION CAUSED BY BACK FLOW EXHAUST ON THE FIRE DETECTOR LOOPS. OPS CHECK GOOD.