Fuel remaining in the tank when the fuel quantity indicator reads zero is:

• A. Not usable
• B. Usable
• C. Fully usable
• D. Partial usable

Answer: (A)

The gauge reflects the amount of fuel that can actually be pumped to the engine—usable fuel. When the indicator reads zero, no usable fuel is left, but there is still a small amount of fuel in the tank that cannot be drawn out by the fuel system due to design limits such as pickup position and suction head. This leftover fuel is called unusable fuel. So, the fuel remaining at zero indication is not usable for flight.