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.