What does the Fuel System Icing Inhibitor test measure?

• A. Percentage of FSII in JP-5
• B. FSII concentration in PPM
• C. FSII mass in grams
• D. Proportion of water in fuel

Answer: (A)

The test is about how much anti-icing additive is in the fuel, expressed as a percentage of the total fuel. Fuel System Icing Inhibitor (FSII) is mixed into JP-5 to prevent ice from forming in the fuel system, especially when water is present. Verifying the FSII amount by percent by volume ensures the fuel batch has the right protection level, regardless of how much fuel you have. Expressing the concentration as percent by volume matches how the specification sets acceptance limits and keeps the measure directly tied to the fuel mix. Using concentration in parts per million would be more cumbersome for the typical FSII ranges and doesn’t reflect the overall fuel-portion proportion the specification uses, while measuring FSII mass in grams would depend on the total batch mass. The test focuses on the FSII amount, not the water content itself, so the proportion of water isn’t what this test reports.