The aircraft was being operated as a flight of two on a ferry flight from the Marshall Islands to Honolulu. The airplane was equipped with auxiliary fuel tanks. About 2 hours after departure, while at an altitude of 7,000 feet msl, the accompanying airplane noticed smoke trailing from the left engine of the Islander. The two aircraft turned around and the pilot declared an emergency. The left engine of N16VM quit and the pilot feathered the propeller. The pilot was unable to maintain level flight and the aircraft was ditched in rough water and subsequently sank. The pilot was rescued about 20 hours afterwards. PROBABLE CAUSE: “An undetermined failure of the left engine. The inability of the airplane to maintain level flight and exceeding the one-engine capability was a factor in the accident.”