As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEVEL 1 "FIRE DET 3 FAIL" ILLUMINATED 5:30 INTO FLIGHT, AT FIRST ALERT WAS INTERMITTENT FOR 15 MINUTES THEN REMAINED STEADY FOR REMAINDER OF FLIGHT. ACCESSED FDCU 3 THROUGH CFDS SHOWED UPPER RT LOOP B FAULT. ADJUSTED ROUTING OF LOOP, RESECURED RESPONDER. PERFORMED R-T-S PASSED. NORMAL OPS IAW MM 26-11-03-4. OK FOR SERVICE. FINAL CLOSED.