What was found
NR 4 ENGINE FIRE FAULT WARNING AND BOTH NACELLE TEMPS READING 8 UNITS. SELECTED "A" LOOP HAD FIRE WARNING BELL AND HANDLE CAUTION LIGHT. PULLED FIRE TEE HANDLE LIGHT AND AURAL WARNING LIGHT EXTINGUISHED/SILENCED. SUSPECT PNEUMATIC LEAK. FIRE BOTTLE WAS NOT DISCHARGED. ON SYSTEM CHECKOUT & INSPECTION, FOUND SHEARED SENSE LINE OFF NR 4 ENGINE MAIN SUPPLY BLEED DUCT. PERFORMED CHAPTER 5 INSPECTION PER MM 5-51-28 & 5-51-32. NO SIGNS OF OVERHEAT. REPLACED SENSE LINE LEAK CHECKED.