B727 FREIGHTER ON DOWNWIND #1 ENG FIRE WARNING. CAPT AND SO COMPLETED THE ENG FIRE CHKLIST AND SHUT THE ENG DOWN; FIRE WARNING OUT. EMER DECLARED AND AFTER CLRING RWY GOT ANOTHER FIRE WARNING SAME ENG. SHUT DOWN ALL ENGS AND EVACED THE ACFT. MAINT FOUND MECHANICAL FAILURE OF THE FIRE WARNING SYS.

Narrative

WE WERE ON A VISUAL APCH INTO GTF ABOUT 2 MI E OF RWY 3 WHEN WE HAD A FIRE WARNING ON ENG #1. THE ACFT WAS CONFIGURED AT FLAPS 5 DEGS WITH THE FO FLYING. I TOLD THE FO TO CONTINUE FLYING THE AIRPLANE AND TO CONTINUE WITH THE APCH TO GTF. THE SO AND I WORKED THE ENG FIRE CHKLIST. AT THE COMPLETION OF THE CHKLIST; #1 ENG WAS SHUT DOWN AND THE FIRE WARNING EXTINGUISHED. THE FIRE WARNING SYS WAS THEN TESTED AND WE HAD A GOOD TEST OF THE SYS. AN EMER WAS DECLARED DURING THIS TIME WITH THE REQUEST FOR EMER EQUIP. AT THIS TIME WE WERE TURNING ONTO FINAL FOR RWY 3 AND DID THE BEFORE LNDG CHKLIST. FO CONTINUED TO FLY AND LANDED THE ACFT. AFTER LNDG WE CLRED THE RWY TO WAIT FOR A VISUAL INSPECTION OF ENG #1. BEFORE WE COULD STOP WE HAD ANOTHER FIRE WARNING ON THE SAME ENG (#1). AT THAT TIME I DECIDED TO SHUT DOWN ALL REMAINING ENGS AND EVAC THE ACFT. AFTERWARDS IT WAS DISCOVERED THAT THE FIRE WARNING WAS CAUSED BY A MECHANICAL FAILURE OF THE FIRE WARNING SYS. THERE WERE NO FIRES. SUPPLEMENTAL INFO FROM ACN 347886: THROUGHOUT MY SO TRAINING (GND SCHOOL; SIMULATOR; AND IOE); AND THROUGH MY FIRST WK OUT OF TRAINING; I HAD NOT SEEN THIS FIRE WARNING TEST SYS. THIS PARTICULAR SYS WAS A 3-WAY TEST SWITCH. UNLIKE THOSE I HAD SEEN IN THE PAST (FIRE WALL; OFF; FIRE WALL AND WHEEL WELL); THIS SYS HAD A SEPARATE TEST FOR SYS A AND ALSO FOR SYS B (SYS A; OFF; SYS B AND WW). IN ADDITION; THE GND FAULT LIGHT TEST WAS ALSO DIFFERENT. ALL OTHER ACFT I HAD SEEN HAD EITHER NO TEST SWITCH FOR THE GND FAULT LIGHTS; OR HAD THE A-AB-B 3-WAY SWITCH. THIS PARTICULAR ACFT HAD A SPRING LOADED TOGGLE SWITCH; A-OFF- B. ON PREFLT I TESTED THE FIRE SWITCH BOTH DIRECTIONS WITH A GOOD TEST. HOWEVER; ON THE ENG SHUTDOWN CHKLIST WHEN I TESTED THE SYS I ONLY MOVED THE SWITCH DOWN (TO TEST WHAT I THOUGHT WAS THE FIRE WALL AND WHEEL WELL). I ALSO LOOKED AT MY AFT PANEL FOR A GND FAULT LIGHT AND HAD NONE -- SO IT APPEARED THE FIRE TEST WAS SATISFACTORY.