Definition
An organic alcohol-based chemical compound added in small quantities to aviation gasoline (avgas) as a fuel system icing inhibitor (FSII) and anti-corrosion agent. It mixes readily with fuel and helps prevent water in the fuel from freezing into ice crystals that could block fuel lines, filters, or carburetor passages.
Plain English
A chemical added to fuel in tiny amounts to stop water in the fuel from turning into ice and to slow corrosion inside the fuel system.
Context Anchor
Seen in fuel system discussions, especially when studying fuel contamination, cold-weather operation, and approved fuel additives.
Derivation
From 'hexylene' (a six-carbon hydrocarbon group, from Greek 'hex' meaning six) and 'glycol' (Greek 'glykys' meaning sweet, the chemical family that includes antifreeze). The name signals what it does in the fuel: it behaves like an antifreeze, just as ethylene glycol does in a car's cooling system.
Why Pilots Care
Without this additive, water in cold fuel can freeze and starve the engine of fuel.
Intuition Check
Hexylene glycol is not ordinary automotive antifreeze for an airplane. In this context, it is a specific approved fuel additive used only as directed.
Example Sentence 1
The fuel additive contained hexylene glycol to prevent ice from forming in the lines during high-altitude flight.
Example Sentence 2
The pilot confirmed the correct amount of hexylene glycol was present before departure.