FAA Powerplant Written Practice Test

If a pilot suspects the onset of vapor lock, which procedure might be helpful?

1. Turn off the auxiliary fuel pump

2. Increase engine throttle

3. Turn on the auxiliary fuel pump

4. Change fuel type

The correct answer is: Turn on the auxiliary fuel pump

In situations where a pilot suspects the onset of vapor lock, turning on the auxiliary fuel pump can help alleviate the problem. Vapor lock occurs when the fuel becomes too hot and turns into vapor, disrupting the normal flow of liquid fuel to the engine. By activating the auxiliary fuel pump, the pressure in the fuel system can be increased, which helps push the vaporized fuel through the lines and back to a liquid state, ensuring a continuous flow to the engine. This can restore normal engine operation by overcoming the obstruction caused by vapor lock. The other options would not address the issue effectively. For example, turning off the auxiliary fuel pump could worsen the situation by reducing fuel flow. Increasing engine throttle might create additional heat and enhance the likelihood of vapor formation. Changing fuel type is not an immediate or practical solution in-flight and could involve risks that compromise safety.