As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUS - CREW REPORTED ABOUT 4 MINUTES AFTER TAKEOFF THE FIRE DETECTOR LOOP AND THE B-LOOP LIGHT ON THE LEFT ENGINE ILLUMINATED. EMERGENCY DECLARED RETURNED AUS LANDED WITHOUT INCIDENT. DURING APPROACH BACK TO THE AIRPORT THE LIGHT ON THE FIRE HANDLE EXTINGUISHED AND THE LOOP LIGHTS ALSO WENT OUT. AIRCRAFT REMOVED FROM SERVICE. REPLACED ANTI-ICE TUBE ON LEFT ENGINE. SYSTEM GROUND CHECKED NORMAL OPERATION.