What does "residual fuel" refer to?

Residual fuel refers to the fuel that remains in the tanks, fuel lines, and engine after draining. This concept is critical in weight and balance calculations because any remaining fuel can contribute to the overall weight of the aircraft, affecting its center of gravity and operational safety.

Understanding residual fuel helps pilots and maintenance crews accurately assess the aircraft's weight before a flight. Calculating the residual fuel can prevent assumptions that the aircraft is lighter than it actually is, leading to improper weight and balance configurations. This is vital to ensure optimal performance, fuel efficiency, and safety standards are maintained.

The other options do not accurately describe residual fuel. Fuel planned for the next flight pertains to expected future use, fuel left after a fill does not consider the operational context of draining, and fuel used during the last operation refers to consumption rather than what remains.