	By 1979, United States Navy and Marine Corps Boeing Vertol CH-46 Sea Knight helicopters had been involved in 64 emergency landings in water. Of the 64, 47 helicopters sunk after landing, killing 75. A study estimated 50% of those fatalities could have been prevented had the helicopters been equipped with adequate emergency flotation. Because helicopters tend to have a high center of gravity due to the high-mounted engine and transmission, even if they are naturally buoyant in the water with hatches secured, they will tend to overturn in heavy sea conditions.