As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
REDUCED EPR TO AT 3000 FT, ALT NR 4 ENG FIRE WARNING WHEN THROTTLE WAS PULLED TO IDLE LT AND BFW WENT OUT RTB TO KGSO. FOUND BLOWN DUCT REMOVED AND REPLACED DUCT IAW MM CHAPTER 75 ENGINE OPS CK GOOD ON ENGINE RUN, NO DEFECTS NOTED ON NR 4 ENGINE.