Definition
The formation of ice within an aircraft's fuel system caused by water suspended or dissolved in the fuel freezing as fuel temperature drops below 0°C. Ice crystals can collect on fuel filters, screens, and lines, restricting or completely blocking fuel flow to the engine. It is most common in turbine aircraft operating at high altitudes for extended periods, where cold-soaked fuel can fall well below freezing.
Plain English
Tiny bits of water in the fuel turn into ice when the fuel gets very cold, and that ice can clog the filters and lines that feed fuel to the engine.
Context Anchor
Seen in fuel system, preflight, cold-weather operations, and engine power-loss discussions.
Why Pilots Care
Unresolved fuel system icing can cause partial or total engine power loss during flight.
Grounding Statement
Even small amounts of water that look invisible in fuel can freeze into ice crystals at altitude and choke off fuel flow before the fuel ever reaches the engine.
Intuition Check
Do not think of icing only as ice on the wings or windshield. Fuel system icing happens inside the fuel system, where the pilot may not be able to see it directly.
Example Sentence 1
After cruising at FL370 for two hours, the crew noticed a rising fuel filter bypass indication, a classic early sign of fuel system icing.
Example Sentence 2
After noticing a gradual power loss in cold conditions, the pilot suspected fuel system icing and applied carburetor heat.