What was found
CREW REPORTED WHILE CRUISING AT 35,000 FEET BETWEEN EWR AND SDF, HAD A MAIN CARGO DECK FIRE WARNING. COULD NOT DETECT ANY FIRE OR SMOKE VISUALLY, UPS EMERGENCY PROCEDURES WERE USED. MADE EMERGENCY DESCENT INTO PIT. FIRE TRUCKS MET THE AIRCRAFT. FIRE TEAM CAME ON BOARD, NO FIRE WAS FOUND. DEFERRED DETECTOR, RETURNED TO SDF.