A Fuel System Icing Inhibitor (FSII) is a manufactured fluid which, when added to aviation fuels, helps to prevent the formation of ice crystals in filters, fuel lines and other fuel system components.
It is extremely important to store Fuel System Icing Inhibitor FSII properly. Drums containing FSII must be kept clean and dry, since the additive is hygroscopic and can absorb water directly from moisture in the air. Since FSII is toxic, a crew member must wear gloves when handling it undiluted. Many FBOs allow Fuel System Icing Inhibitor FSII injection to be turned on or off so that one fuel truck can service planes that do require Fuel System Icing Inhibitor FSII as well as planes that don't. Line crew, however, must be able to deliver FSII when it is needed.
