What is the danger of using fuel that vaporizes too readily?

• A. Vapor lock is a rare issue with aviation engines.
• B. Vapor lock can occur in the fuel lines, shutting off the flow of fuel to the engine.
• C. Vapor lock occurs only in high-altitude operations.
• D. Vapor lock is not related to fuel flow.

Answer: (B)

When fuel vaporizes too readily, it can form gas bubbles in the fuel system. Those bubbles create vapor lock, which blocks the flow of liquid fuel to the engine. Since the engine relies on a continuous supply of liquid fuel, the presence of vapor prevents the pump from delivering fuel properly, starving the engine and potentially causing power loss or an engine quit.

This is why the best answer is that vapor lock can occur in the fuel lines, shutting off the flow of fuel to the engine. It’s not a rare issue, it isn’t limited to high-altitude operation, and it is fundamentally related to fuel flow, so the other statements don’t fit.