FAA Ground School Practice Test

Why is filling the fuel tanks after the last flight of the day considered a good practice?

1. It helps in fueling more efficiently

2. It cools the tanks

3. It prevents moisture condensation by eliminating airspace

4. It allows for quicker startup the next day

The correct answer is: It prevents moisture condensation by eliminating airspace

Filling the fuel tanks after the last flight of the day is considered a good practice primarily because it prevents moisture condensation by eliminating airspace in the tanks. When fuel tanks are left partially empty, the empty space allows for air to fill the tank. Changes in temperature can cause this air to expand and contract, which can lead to condensation forming inside the tank. This condensation can introduce moisture into the fuel system, potentially causing fuel contamination and other operational issues. By filling the tanks completely, the amount of air in the tank is minimized, which significantly reduces the risk of moisture accumulating inside. This practice helps to maintain fuel quality and ensures better performance and reliability of the aircraft during subsequent flights. Additionally, having a full tank can enhance safety by maximizing fuel availability, which can be particularly important for long flights or unexpected delays.