What was found
IN FLIGHT, HAD FLOWN APPROXIMATELY 12 MINUTES OUTBOUND, THEN HEARD GONG AND HAD ENGINE FIRE LIGHT INTERMITTENTLY. TURNED AROUND TO RETURN TO ICY AND LIGHT WENT OUT. ON FINAL TO ICY, LIGHT CAME BACK ON STEADY FOR 3 TO 5 SECONDS THEN WAS INTERMITTENT. MAINTENANCE CLEANED BOTTOM FIRE DETECTOR AND REMOVED UPPER REAR FIRE DETECTOR AND INSTLALED SERVICEABLE FIRE DETECTOR, FUNCTION CHECKED GOOD. (M)