What was found
IAH - FLT 1876 - THE NR 1 ENGINE FIRE BELL AND LIGHT ACTIVATED AFTER TAKEOFF FROM IAH. THE ENGINE WAS RUN IN IDLE AND THE NR 1 BLEED WAS TURNED OFF. THE FIRE WARNING CEASED. THE AIRCRAFT WAS RETURNED TO IAH WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE NR 1 ENGINE 8TH STAGE PNEUMATIC DUCT RUPTURED BETWEEN CHECK VALVE AND FIREWALL. THE DUCT WAS REPLACED. THE FIREWALL FIRE LOOP WAS REPLACED DUE TO HEAT DAMAGE. THE NR 1 ENGINE WAS RUN AND OPEATION CHECKED GOOD WITH NO LEAKS FOUND. (X)