What was found
ON DESCENT TO MSP, THE NR 2 ENGINE FIRE WARNING SYSTEM ACTIVATED MOMENTARILY. A PRECAUTIONARY SHUTDOWN WAS ACCOMPLISHED ON NR 2 ENGINE. THE FLIGHT CONTINUED TO MSP AND LANDED WITHOUT FURTHER INCIDENT. A LEAK WAS FOUND IN THE NR 3 START BLEED AIR DUCT. MAINTENANCE REPLACED THE DUCT AND CHECKED THE SYSTEM FOR LEAKS, NONE FOUND. OPERATIONAL CHECKS WERE OK, AIRCRAFT RETURNED TO SERVICE.