FAA Ground School Practice Test

What type of fuel can be substituted if the recommended octane is not available?

1. The same octane aviation gas

2. A lower grade of fuel

3. The next higher octane aviation gas

4. Automotive fuel

The correct answer is: The next higher octane aviation gas

When the recommended octane fuel is not available, using a higher octane aviation gasoline is the appropriate substitute. Higher octane fuel can help prevent engine knocking and maintain performance, particularly during operations requiring high power levels, such as takeoff and climb. It's essential to ensure that the aircraft engine can safely operate with the higher octane fuel, as this can help prevent damage that could arise from using fuel with insufficient octane ratings, which would not effectively support the engine's requirements. Choosing a lower grade of fuel could lead to engine performance issues and potentially dangerous situations due to knocking or pre-ignition. Utilizing automotive fuel is not recommended either, as it may contain additives that are harmful to aircraft engines. Thus, opting for the next higher octane aviation gas ensures the engine operates efficiently while still adhering to safety standards.