March 25/14-The Discovery Air Defence Services Dornier Alpha Model A (C-FOTA) was operating as CHETA61 on a local flight from Ottawa M-CIA (CYOW). While performing aerial work at Petawawa the pilot received RH OIL light and Master Caution indications. The throttle was reduced and the engine shut down. (SNECMA LARZAC C6). An emergency was declared with ATC and the aircraft landed at Ottawa uneventfully with ARFF standing by. Preliminary findings indicate an engine plug had come off in flight. The company is conducting a detailed review.