What was found
(CAN) WHILE ENROUTE, WE HEARD NR 2 ENGINE FIRE TONE. THE FIRE CAUTION LIGHT INDICATOR WAS LIT AS WELL. WE THEN PROCEEDED WITH THE IMMEDIATE ACTION PRESCRIBED IN THE EMERGENCY PROCEDURE. THE FIRE INDICATOR C/L WAS STILL ON AFTER MAIN BOTTLE WAS DISCHARGED. AFTER THE TIME PRESCRIBED, WE ACTIVATED THE RESERVE. C/L FIRE INDICATOR WENT OUT. AFTER EVALUATION, ON ARRIVAL OF THE AME, NO EVIDENCE OF FIRE WAS FOUND AND THE SYSTEM TESTED NORMALLY IAW THE FLIGHT MANUAL & THE MM. THE WIRING WAS VISUALLY INSPECTED, MANUALLY SHAKEN TO DETECT ANY POSSIBLE INTERMITTENT PROBLEM AND THE FAULT COULD NOT BE REPRODUCED. THE MOST PROBABLE CAUSE WAS DETERMINED TO BE A BAD INTERMITTENT OLD STYLE FLAME DETECTOR. NOTE THAT THE DETECTORS ARE TESTED DURING EACH 300 HR INSPECTION AND THE LAST TEST WAS DONE 181 HOURS PRIOR TO THE INCIDENT. ALL 4 FLAME DETECTORS WERE UPGRADED FROM, -101 TO -104, AND CSN 76-178 WAS ALSO INCORPORATED INTO THE ACFT TO IMPROVE THE RELIABILITY OF THE SYS. MARCH 20, 2013, THE SUSPECTED REMOVED FLAME DETECTORS WERE RE-TESTED BY CONNECTING THEM TO THE ACFT AND RISING THEIR TEMPERATURE WITH A HEAT GUN TO SEE IF THE PROBLEM COULD BE REPLICATED. NO PROBLEM WAS FOUND. WE ARE EXPECTING MORE INFORMATION FROM MFG CONCERNING COST AND AVAILABILITY FOR A POSSIBLE OFFICIAL LAB TESTING OF THESE FLAME DETECTORS.