FAA Sport Pilot Airplane (SPA)Aircraft Performance and SystemsMedium
After landing on a hot day, a pilot with a fuel-injected engine has difficulty restarting the engine. The fuel in the fuel lines has become heated enough to form vapor bubbles that block proper fuel flow to the engine. This condition is known as
- Adetonation
- Bcarburetor icing
- Cpre-ignition
- Dvapor lock
Show answer & explanationAnswer & explanation
Correct answer: D. vapor lock
Vapor lock occurs when fuel in the lines gets hot enough to boil and form vapor bubbles, which interrupt the steady flow of liquid fuel to the engine. It is more common in fuel-injected engines and on hot days shortly after shutdown, when residual engine heat soaks into the fuel lines.
Why the other options are wrong
- A. Detonation is uncontrolled explosive combustion of the fuel-air mixture in the cylinder, not a fuel delivery issue.
- B. Carburetor icing occurs due to evaporative cooling in the carburetor venturi, typically affecting carbureted, not fuel-injected, engines.
- C. Pre-ignition is combustion starting before the spark plug fires, usually due to a hot spot in the cylinder.
Vapor Lock
A condition where fuel boils in the fuel lines due to heat, forming vapor bubbles that block or restrict fuel flow to the engine.
- More common in fuel-injected engines and hot weather
- Often occurs after shutdown when engine heat soaks into fuel lines
- Can cause hard starting or engine stoppage
- Different from carburetor icing, which involves cooling, not heating
Memory trick: Vapor lock: fuel gets so hot it turns to gas bubbles, locking out flow