What was found
(CAN) WHILE DOING AIRBORNE SURVEY WORK (BIRD TOWING), ENGINE CHIP LIGHT ILLUMINATED. HELICOPTER DESCENDED TO VALLEY BOTTOM AND MADE A PRECAUTIONARY LANDING. UPON LANDING, THE ENGINE MOMENTARILY DECELLERATED AND THEN RE-ACCELERATED. ENGINE WAS SHUTDOWN AND RAPIDLY DECELERATED ACOMPANIED BY A GRINDING/RUBBING NOISE. POST FLIGHT INSPECTION REVEALED A LARGE AMOUNT OF METAL CHIPS ON THE ENGINE CHIP PLUGS. ENGINE REMOVED AND SENT TO MFG FOR FURTHER INVESTIGATION.