As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 4801 - AFTER TAKEOFF, NR 1 ENGINE B FIRE DETECTOR LOOP LIGHT CAME ON. SELECTED A LOOP TESTED SYSTEM, SYSTEM TESTED OK. DECIDED TO RETURN TO AIRPORT. REPLACED PRSOV DEACTIVATON VALVE SENSING LINE PE MM. CHECKED SYSTEM AND TESTED OK. (M)