What was found
(CAN) IN CRUISE FLIGHT, NR2 CHIP DETECTOR LIGHT ILLUMINATED. LIGHT PULSED OUT BUT RE-ILLUMINATED MINUTES LATER AND WOULD NO LONGER PULSE OUT. PRECAUTIONARY ENGINE SHUT-DOWN WAS CARRIED OUT AND 3 ENGINE LANDING CARRIED OUT. MAINTENANCE FOUND FERROUS PARTICLES ON MAG PLUG. SUSPECT METAL CONTAMINATION AT LAST OVERHAUL. PLUGS WERE CLEANED AND ENGINE GROUND AND PRFORMANCE RUN CARRIED OUT. AIRCRAFT RETURNED TO SERVICE WITH A 40 FLIGHT HOUR MAINTENANCE WATCH.