Ice begins forming on the outside of the fuel tank in flight. This would most likely be caused by which condition?

• A. Vaporized fuel instead of liquid fuel being drawn from the tank into the main burner
• B. Water condensation at altitude
• C. Ice accumulation from ambient humidity
• D. Liquid fuel freezing in the line

Answer: (A)

Ice on the outside of the fuel tank in flight is most likely caused by drawing vapor from the tank rather than liquid fuel. When fuel is drawn as vapor, the pressure drop through the regulator causes liquid propane to flash into gas, which absorbs heat and chills the tank surface. That cold surface cools any moisture in the surrounding air, causing frost to form on the tank. If liquid fuel were being drawn, the cooling would be much less and frost would be unlikely. The other options involve humidity or line freezing but don’t explain the frost on the tank surface as directly as vapor withdrawal does.