A fuel that vaporizes too readily may cause which problem in aircraft systems?

• A. Vapor lock
• B. Hard starting
• C. Detonation
• D. Engine overheating

Answer: (A)

Vapor lock occurs when fuel in the lines or components turns into vapor and blocks the flow of liquid fuel to the engine. If the fuel is highly volatile, it readily forms vapor in hot conditions or along long fuel lines, creating vapor pockets the pump can’t push, which drops fuel pressure and can cause the engine to stumble, lose power, or quit. That direct relationship between excessive volatility and interrupted liquid-fuel delivery is why vapor lock is the correct choice. Detonation is premature ignition inside the cylinders and isn’t caused by vapor in the fuel lines. Hard starting and engine overheating stem from other issues such as ignition or cooling problems, not the vapor forming in the fuel system.