As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
OUTBOUND LEVEL AT 3000' THE AIRCRAFT BEGAN TO GIVE INTERMITTENT APU FIRE WARNINGS. THE AIRCRAFT WAS TURNED BACK TO RETURN TO BASE AND THE FIRE WARNINGS STOPPED APPROXIMATELY 5 MINUTES AFTER IT HAD BEGUN. WHILE ON APPROACH WHEN THE AIRCRAFT ENTERED CLOUDS THE WARNINGS BEGAN AGAIN AND LASTED UNTIL SHUTDOWN. MAINTENANCE ACTION: REPLACED APU FLAME DETECTOR. OPS CHECKED SATISFACTORY.