What was found
LOWER AFT BODY OVERHEAT ILLUMINATED IN FLIGHT AT FL280. ACCOMPLISHED LOWER AFT BODY OVERHEAT LIGHT ILLUMINATED (CHECKLIST) IAW QRH INDICATED SOURCE OF OVERHEAT AS ENGINE NR 3 LOW STAGE BLEED AIR SUPPLY TO THE MAIN WING ANTI-ICE VALVE. LIGHT EXTINGUISHED AND TESTED GOOD. TESTS NORMAL. RAN ENGINES IWA JRH APPROX 1 HR. REMOVED ACCESS PANEL FOR KEELBEAM AREA. INSPECTED FOR LEAKS WITH LASER HEAT DETECTOR IN AFT STAIRWELL,AFT CGO COMPARTMENT, KEELBEAM AREA, FOUND NONE. CHECKED FOR CLEARANCE ON ACCESSIBLE LOOPS. FOUND OK. INSTALLED KEEL BEAM ACCESS PNL. PRIOR HISTORY SHOWS T/S FOR FALSE ALARM. PERFORMED IAW MM 26-14-000-1 HAS BEEN C/W. REPLACED DET CONT. IAW MM. TESTS OK.