What does 'unusable fuel' refer to, and how is it treated in some data sets?

• A. Unusable fuel is fuel you can burn; it is always excluded from balance calculations.
• B. Unusable fuel is the portion of fuel that cannot be burned; depending on the data set, it may be included in BEW or listed separately for balance calculations.
• C. Unusable fuel is fuel that can be used only for ballast.
• D. Unusable fuel is fuel that is used for engine testing.

Answer: (B)

Unusable fuel is the portion of fuel in the tanks that cannot be burned during flight. It still adds weight and a specific lever arm, so it affects the aircraft’s weight and balance even though it isn’t consumable fuel.

In some data sets this mass is included with the Basic Empty Weight, meaning the BEW already accounts for it. In other data sets it’s listed separately as unusable fuel so you can include its weight and moment explicitly in your balance calculations. Either way, it’s not counted as usable fuel, but it does impact takeoff weight and center of gravity.

Why the other ideas don’t fit: it isn’t fuel you can burn, so it isn’t always excluded from balance; it isn’t something used only for ballast, and it isn’t specifically fuel used for engine testing.