What was found
FLT 2031 - MHR - AFTER TAKEOFF, ALL CARGO SMOKE DETECTORS EXCEPT NR 1 AND NR 3 ILLUMINATED. WHILE DUMPING FUEL TO REDUCE TO LANDING WEIGHT SOME DETECTORS WENT OUT AGAIN, THEN ALL CAME ON AGAIN. AIRCRAFT MADE UNEVENTFUL LANDING AT MHR. INSPECTED CARGO COMPARTMENT FOR EVIDENCE OF SMOKE. NONE FOUND. INSPECTED CARGO CANS FOR EVIDENCE OF SMOKE, NONE FOUND. PERFORMED ENGINE RUN AT T/O POWER WITH PACKS ON AND GEN ONLINE. ALL SMOKE DETECTORS, OPS CHECK NORMAL. GROUND CHECK GOOD. AIRCRAFT RETURNED TO SERVICE. (M)