It's been about two decades since general aviation adopted 100-octane, low-lead avgas, and plane makers say the need for unleaded fuel has become intense. Besides environmental concerns over emissions from tens of thousands of piston aircraft, there is also the issue of availability. Only one major supplier produces the additive needed for all of the world's piston aircraft, so an interruption in supply -- or a sharp increase in price -- could wreak havoc. The two most likely replacements for today's avgas both come with unique disadvantages. An unleaded, petroleum-based fuel would require physical modifications of high-performance aircraft, while synthetic biofuels require further testing and proof they can meet demand.
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