As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INTERMITTENT FIRE WARNING INDICATION ON APU DURING FLIGHT. PULLED A LOOP CB FOR APU FOR FIRE WARNING SYSTEM WHICH STOPPED INTERMITTENT FIRE WARNING. FOUND WIRING ON APU A LOOP FIRE WARNING CONNECTION CHAFING WITH STRUCTURE. REPAIR PER STANDARD PRACTICE 20-3--22, OPS CHK OK PER MM 26-25-00.