Vapour lock
Vapour lock is fuel changing from liquid to gas while still in the fuel delivery system (PHAK Glossary).
- Effect: gas disrupts fuel pump, dropping feed pressure to carburettor or fuel injection system.
- Result: transient power loss or complete stalling. Restart may be difficult.
- Causes:
- Fuel heated by engine
- Fuel heated by local climate (hot day)
- Fuel boils at lower temperature at high altitude
- Fuel-injected engines: ground operations on hot days can heat fuel until it vaporizes in the line, so it never reaches the cylinders (PHAK ch.7).
Trap: vapour lock is fuel boiling in the lines, not water or ice blocking them; high altitude lowers boiling point, does not raise it.
References
- FAA-H-8083-25 PHAK Glossary (Vapor lock)
- FAA-H-8083-25 PHAK ch.7 (Fuel Selectors)