How can fuel become contaminated?

Fuel contamination can occur primarily through the introduction of water and dirt during the fueling process. When fuel is transferred, whether from a storage tank to the aircraft or during transport, there are various opportunities for contaminants to enter the fuel. Water can condense within fuel tanks, particularly in humid conditions, and can create problems such as fuel separation and engine performance issues. Similarly, dirt and sediment can mix with the fuel during any point of handling, whether during pumping or filling.

In contrast to this understanding, the other options might seem appealing but do not contribute to fuel quality. High-quality fuel, while essential, does not inherently protect against contamination when water or dirt is introduced in the process. Using a filter is useful for capturing particles during the transfer but does not prevent contamination from occurring if the water or dirt is already present in the fuel source. Lastly, keeping fuel tanks at maximum capacity helps reduce the space for condensation but does not eliminate the risk of contamination during refueling or improper storage practices.