What was found
THE 1 ENGINE FIRE WARNING LIGHT ILLUMINATED ON TAKEOFF ROLL AT APPROXIMATELY 120 KNOTS. THE ENGINE FAIL/FIRE CHECKLIST WAS ACCOMPLISHED. THE FIRE LIGHT WENT OUT APPROXIMATELY 10 SECONDS AFTER RETARDING THE NR 1 THROTTLE. THE NR 1 ENGINE B-LOOP LIGHT WAS STILL ILLUMINATED. THE SYSTEM TESTED VALID WHEN SWITCHED TO A. MAINTENANCE FOUND THE NR 1 ENGINE HIGH STAGE PNEUMATIC DUCT SEPARATED WITH RESULTING DAMAGE TO BOTH THRUST REVERSER COWLS. REMOVED AND REPLACED THE PNEUMATIC DUCT, THE LT AND RT FAN REVERSERS. A POWER ASSURANCE RUN WAS PERFORMED, OPERATION CHECKED GOOD.