Definition
A grade of leaded aviation gasoline with a minimum lean-mixture octane rating of 80, dyed red, intended for low-compression piston aircraft engines that do not require higher-octane fuels. It contains a small amount of tetraethyl lead and is sometimes labeled 80/87, where the second number reflects performance under rich mixture conditions.
Plain English
A specific type of aviation fuel for piston-engine aircraft. The number 80 tells you how much engine pressure it can handle before causing knocking. It is colored red so pilots can recognize it on sight.
Context Anchor
Seen in fuel-grade charts, aircraft fuel placards, and operating handbook fuel requirements.
Derivation
AVGAS is short for 'aviation gasoline.' The number 80 refers to the octane rating — a measure of how much compression the fuel can take before it spontaneously ignites (knocks). Higher numbers mean the fuel resists knocking better, which lets engines run at higher compression and produce more power.
Why Pilots Care
Using the correct fuel grade prevents engine damage such as detonation, overheating, or power loss.
Intuition Check
Do not read “80” as 80 percent gasoline or 80 gallons. In AVGAS 80, the number is the fuel grade, showing its resistance to engine knock.
Example Sentence 1
The older trainer's POH listed AVGAS 80 as the approved fuel, but the FBO only stocked 100LL, so the pilot checked the supplement for an approved alternative.
Example Sentence 2
The fuel truck delivered AVGAS 80 into the wing tanks of the low-compression trainer before the student flight.