FAA Commercial Pilot Airplane (CAX)Aircraft SystemsMedium
A pilot attempts a hot engine start on a fuel-injected airplane shortly after shutdown, but the engine will not start reliably. This difficulty is most likely caused by:
- Adetonation in the cylinders from excessive heat
- Ban overboosted turbocharger from residual exhaust heat
- Ccarburetor icing from evaporative cooling
- Dvapor lock, caused by fuel vaporizing in the lines due to residual engine heat
Show answer & explanationAnswer & explanation
Correct answer: D. vapor lock, caused by fuel vaporizing in the lines due to residual engine heat
Fuel-injected engines route fuel lines close to hot engine components. After shutdown, heat soak can vaporize fuel in the lines, creating vapor lock that prevents proper fuel delivery for a hot start, unlike carburetor systems which draw fuel through cooler intake air.
Why the other options are wrong
- A. Detonation occurs during combustion, not during starting attempts.
- B. Turbocharger overboost relates to manifold pressure during operation, not starting difficulty.
- C. Carburetor icing cannot occur in a fuel-injected engine, which has no carburetor.
Vapor Lock (Fuel Injection)
A condition where fuel vaporizes in injection lines due to engine heat soak, disrupting fuel flow and causing hard hot starts.
- More common in fuel injection than carburetion
- Caused by heat soak after shutdown
- Mitigated by proper hot-start procedures (e.g., mixture/throttle technique)
Memory trick: Hot lines boil the fuel — vapor lock locks out the start.