Fuel system icing inhibitor (FSII) is an additive to aviation fuels that prevents the formation of ice in fuel lines. FSII is sometimes referred to by the registered, genericized trademark PristJet fuel can contain a small amount of dissolved water that does not appear in droplet form. As an aircraft gains altitude, the temperature drops and Jet fuel’s capacity to hold water is diminished. Dissolved water can separate out and could become a serious problem if it freezes in fuel lines or filters, blocking the flow of fuel and shutting down an engine. In other words a fuel anti-icing additive for turbine fuel that acts as a fuel icing inhibitor. ICE-5 is mixed in the fuel at rates of 0,10% up to 0,15% by volume. If the aircraft has no heating system for the fuel, small amounts of free water in the fuel can freeze and block fuel lines, filters and valves. Properly used ICE-5 will prevent icing of the water in the fuel system. A positive side effect of ICE-5 is inhibition of bacteria-growth in fuel tanks.