BEECH 1900D ACFT ON APCH IN CHOPPY AIR HAD INTERMITTENT FIRE LOOP WARNINGS; THEN THE FIRE T HANDLE FOR THE L ENG FLASHED INTERMITTENTLY. FLC XCHKED ALL ENG INSTS AND DETERMINED THE WARNINGS TO BE FALSE AND PROBABLY RELATED TO THE CHOPPY AIR. POSTFLT EXAMINATION REVEALED A BROKEN FIRE LOOP. THE WARNINGS CEASED WHEN THE ACFT EXITED THE CHOP.

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THIS INCIDENT OCCURRED IN A BEECH 1900D. I WAS THE PF. WE WERE BEING VECTORED ON BASE LEG FOR THE ILS 27L AT SBN. THE ALT WAS 4000 FT AND WE WERE NEAR THE TOPS OF A CLOUD LAYER (WHICH WAS CAUSING LIGHT CHOP). OUT OF THE CORNER OF MY EYE I KEPT SEEING AN AMBER ANNUNCIATOR FLASH ON AND OFF. IT WAS ENOUGH TO SET OFF THE MASTER CAUTION LIGHT; BUT AT FIRST IT DID NOT STAY ON LONG ENOUGH TO TELL WHAT IT WAS. I KEPT MY EYE ON THE CAUTION ADVISORY PANEL. AT FIRST I THOUGHT IT WAS A 'NO AUX XFER' LIGHT WHICH INDICATES THAT THERE IS NO FUEL XFER FROM AUX TO MAIN FUEL TANKS. HOWEVER; THIS SYS; WHICH USUALLY GIVES THIS KIND OF INDICATION IN TURB; WAS NOT ON. FINALLY I NOTICED THAT IT WAS AN 'L FIRE LOOP' AMBER ANNUNCIATOR WHICH WAS FLASHING. THIS LIGHT INDICATES THAT THE INTEGRITY OF THE ENG FIRE DETECTION SYS HAS BEEN COMPROMISED. AT THAT POINT IT MAY OR MAY NOT INDICATE AN ENG FIRE. IT BEGAN TO FLASH MORE OFTEN (ABOUT EVERY OTHER SECOND FOR 1/2 - 1 SECOND AT A TIME). THEN ABOUT 20 SECONDS AFTER IT BEGAN; THE L FIRE T HANDLE BEGAN TO FLASH ON AT 1/2 SECOND INTERVALS. THE T HANDLE WOULD FLASH ON ABOUT ONCE EVERY 10-15 SECONDS AND REMAIN ILLUMINATED LONG ENOUGH TO SET OFF THE MASTER WARNING LIGHT. THE FO AND I NOTED NO SECONDARY INDICATION OF AN ENG FIRE: NORMAL OIL TEMP AND PRESSURE (SAME AS R SIDE); NORMAL ENG PWR INDICATIONS (WITHOUT FLUCTUATION AND MATCHED TO THE R SIDE); AND NO VISUAL SIGNS OF SMOKE OR FIRE. AS WE INTERCEPTED THE ILS AND DSNDED TO 2300 FT MSL THE TURB DECREASED AND ALL ANNUNCIATORS EXTINGUISHED FOR THE REMAINDER OF THE FLT (ABOUT 4 MINS). WE ELECTED NOT TO SHUT DOWN THE ENG OR REQUEST PRIORITY HANDLING FROM ATC BECAUSE WE BOTH AGREED THAT IT WAS A FAULTY FIRE INDICATION. AFTER LNDG IT WAS CHKED BY A LCL MECH. IT SEEMS THAT THE CONTINUOUS LOOP FIRE DETECTION SYS HAD BROKEN FROM VIBRATION. THE BREAK WAS 2 INCHES AFT OF THE WALL THAT SEPARATES THE HOT SECTION FROM THE ACCESSORY SECTION. THE TURB CAUSED THE BREAK TO INTERMITTENTLY GND FAULT SETTING OFF THE T HANDLE. TO THE BEST OF MY KNOWLEDGE; NO FARS WERE BROKEN IN THIS SIT. FROM THE FIRST AMBER ANNUNCIATOR TO THE LAST ONE; LASTED ABOUT 2 MINS.