FSII additives primarily prevent icing in which components?

• A. Engine lubricating system.
• B. Airframe fuel system, engine fuel filter, or engine fuel control.
• C. Hydraulic power unit.
• D. Electrical generator.

Answer: (B)

FSII additives are used to prevent icing where fuel and water can mix in the fuel system. They work by lowering the freezing point of any water in the fuel and by forming a protective film on metal surfaces to reduce ice adhesion, keeping fuel flow open in cold conditions. The parts most at risk are the airframe fuel system, the engine fuel filter, and the engine fuel control, because they are directly in the fuel path and ice there can block flow or disrupt metering. Other systems, like the hydraulic power unit or the electrical generator, use different fluids (hydraulic oil or lubricants) and aren’t affected by FSII in the same way, so icing prevention for those isn’t addressed by this additive.