What was found
FORTY MINUTES INTO FLIGHT RECEIVED A LEVEL ONE "FIRE DET 1 FAULT" ALERT IT WAS FOLLOWED BY INTERMITTENT LEVEL THREE NR 1 FIRE ALERT AND "FIRE DET 1 FAIL" ALERTS. DECLARED EMERGENCY AND RETURNED TO DEPARTURE. CFDS SHOWS NOT CURRENT FAULTS FOR FDCU 1. LEG 1 FAULTS SHOWS "UP RIGHT FIRE DET ASSY B", UP RIGHT ASSY A". LEG 2 FAULT SHOWS "LOWER FIRE DET ASSY A". REPLACED NR 1 ENG UPPER RT LOOP ASSY AND LOWER TURBINE RAIL ASSY IAW AMM 26-11-03-4-1. REPLACED LT HARNESS ASSY IAW 71-50-04-4-1. REPLACED SEMI RIGID CABLES IAW AMM 71-50-04-2-1. FDCU 1 SHOWS NO CURRENT FAULTS. RTS PASS. AWAITING HIGH POWER ENG RUN. PERFORMED HIGH POWER ENGINE RUN IAW JRH. NO FIRE DETECTION FAULT OR ALERT. NO CURRENT FAULT AFTER ENGINE SHUTDOWN. ACFT OK FOR CONTINUE SERVICE.