ACFT EQUIP PROB WITH FALSE ALARM RETURNS LANDS. TWICE.

Narrative

ON CLBOUT FROM CANCUN; MEXICO; WE EXPERIENCED A VERY SHORT RING ON THE FIRE BELL. ABOUT A MIN LATER; WE HEARD IT AGAIN ONLY THIS TIME IT WAS ACCOMPANIED BY A QUICK FLICKER OF #2 ENG FIRE LIGHT. SHORTLY; IT STARTED TO RING ERRATICALLY AND THE LIGHT FLICKERED. THE BELL WOULD RING IN EXTREMELY SHORT BURSTS AT ERRATIC INTERVALS AND WOULD NOT SILENCE. WE SHUT #2 ENG DOWN USING THE EMER ENG FAILURE FIRE CHKLIST AND RETURNED TO CANCUN TO MAKE AN UNEVENTFUL LNDG. WE THEN HAD 2 MAINT MEN CHK THE PROB OUT FOR 4 HRS BACK IN CANCUN. THEY ALSO CONSULTED WITH ACR MAINT BACK IN HEADQUARTERS. THEY COULD FIND NOTHING WRONG AND ALL WARNING SYS TESTED GOOD. THEY CONCLUDED THAT IT MUST BE A TEMPORARY SHORT IN THE SYS; BUT IT WAS NOW PRESENTLY GOOD. I'M NOT SURE WHAT THE FINAL CORRECTIVE ACTION WAS EXACTLY; BUT MAINT IN HEADQUARTERS GAVE THEIR FINAL APPROVAL; AND WE TOOK OFF AGAIN ONLY TO HAVE THE SAME THING HAPPEN. I INFORMED THE CAPT THAT WE DID HAVE 2 FIRE LOOPS AND ONE COULD BE SHORTING OUT AND THAT WE COULD ISOLATE IT BY USING THE CIRCUIT BREAKERS FOR A AND B SYS. WE DID THAT AND THE PROB STOPPED AND WE RETURNED TO CANCUN. AT NO TIME DID WE PULL BOTH CIRCUIT BREAKERS AT THE SAME TIME SO WE STILL HAD FIRE PROTECTION. WE HAD MAINT CONFIRM THE PROB ON THE GND AND SIGNED OFF THE CORRECTIVE ACTION WITH A DEFERRAL IN CONSULTATION WITH HEADQUARTERS MAINT. WE THEN PROCEEDED ON TO MEM WITH NO FURTHER PROBS.