What was found
PHX - AIR TURNBACK - FLT 0081 - O - ON TAKEOFF OUT OF PHX EN ROUTE TO BWI THE NR 1 ENGINE FIRE WARNING SYSTEM ACTIVATED WITH THE FIRE SWITCH HANDLE ILLUMINATING, A RED MASTER WARNING LIGHT, A RED FIRE LIGHT ON INSTRUMENT PANEL, A RED FUEL CONTROL SWITCH, THE FIRE BELL SOUNDING, AND EICAS MESSAGE FOR FIRE/OVERHEAT NR 1 ENGINE. AUTO THROTTLES WERE SELECTED TO OFF AND THE THROTTLE LEVER RETURNED TO CLIMB; WITH THROTTLE LEVER IN CLIMB WARNING MESSAGES CLEARED. AN EMERGENCY WAS DECLARED AND AIRCRAFT LANDED SAFELY BACK AT PHX. WHEN MX EXAMINED THE NR 1 ENGINE THE HIGH PRESSURE DUCT WAS FOUND DISCONNECTED, HEAT DAMAGE WAS NOTED TO THE PYLON, C-DUCTS, AND SURROUNDING AREA.