Residual fuel is defined as the fuel remaining in which parts after draining?

• A. The fuel remaining in the tanks after draining
• B. The fuel remaining in the tanks, lines, and engine after draining
• C. The fuel that cannot be burned
• D. The fuel used in flight

Answer: (B)

Residual fuel is the fuel that remains in the entire fuel system after draining, including the tanks, the lines, and the engine. This accounts for fuel that can stay trapped in pipelines and combustion components even after a draining procedure, and it matters in weight and balance because it adds to the aircraft’s remaining weight and can affect center of gravity. The option that includes tanks, lines, and engine captures all parts of the fuel system that can retain fuel after draining, making it the correct definition. The other descriptions are incomplete or off the mark: only tanks misses the fuel that remains in lines and the engine; describing it as fuel that cannot be burned doesn’t fit how residual fuel is defined for draining purposes; and the fuel used in flight is what is consumed, not what stays behind after draining.