Definition
An aviation gasoline (avgas) grade with an octane rating of 100 and a reduced tetraethyl lead content compared to 100LL. It is dyed blue, like 100LL, and is approved as a direct replacement in piston aircraft engines that are certified for 100LL.
Plain English
A type of aircraft fuel that works the same as the common blue 100LL fuel but contains even less lead. Engines approved for 100LL can use it without any changes.
Context Anchor
Seen in fuel grade discussions, aircraft fuel placards, fuel truck markings, and pilot operating handbook fuel requirements.
Derivation
The '100' refers to the fuel's octane rating, which measures resistance to detonation. 'VLL' stands for 'Very Low Lead,' indicating a lead content lower than 100LL ('Low Lead'). The naming follows the same pattern as other avgas grades, so the letters describe the lead level relative to older, higher-lead fuels.
Why Pilots Care
Permits continued use of high-compression engines with lower environmental lead emissions and reduced spark plug and valve deposits.
Intuition Check
Very low lead does not mean unleaded. 100VLL still contains lead; it just contains less lead than 100LL.
Example Sentence 1
The FBO's fuel truck was placarded for 100VLL, which the mechanic confirmed was approved for our engine in place of 100LL.
Example Sentence 2
Mechanics noted cleaner combustion chambers after switching the fleet to 100VLL.