The Strange Story of Leaded Aviation Gasoline

While leaded gasoline began to be phased out as a motor fuel in the 1970s and has been banned by most developed countries for twenty years or more, most piston powered general aviation craft continue to use avgas with the “100LL” formulation: 100 octane “low lead”, meaning half the lead content of the traditional “100/130” fuel. It is estimated that planes using 100LL gasoline release around 100 tonnes of lead into the environment per year.

Why is this? Think of it as safetyland vs. safetyland. Everybody knows about the hideous toxicity of lead, with symptoms of acute exposure to tetraethyl lead (TEL) including “irritation of the eyes and skin, sneezing, fever, vomiting, and a metallic taste in the mouth. Later symptoms of acute TEL poisoning include pulmonary edema, anemia, ataxia, convulsions, severe weight loss, delirium, irritability, hallucinations, nightmares, fever, muscle and joint pain, swelling of the brain, coma, and damage to cardiovascular and renal organs” and chronic exposure leading to “memory loss, delayed reflexes, neurological problems, insomnia, tremors, psychosis, loss of attention, and an overall decrease in IQ and cognitive function”.

So why do piston powered airplanes continue to use leaded fuel? Well, there’s a whole safetyland tower of bureaucracy surrounding anything having to do with aviation, the grinding of whose gears makes a glacier seem positively spritely. Although many newly-designed light aircraft are certified to run on unleaded automobile gasoline and modification kits have been approved for a few existing planes, the vast majority of light planes in service still require leaded fuel and are prohibited by regulations from using anything else. Because safety, of course.


Midgley had a remarkable career and screwed up more than leaded gasoline:
“An Instinct for the Regrettable”: The Inventions and Legacy of Thomas Midgley, Jr.


We had a post here about the career of Thomas Midgley, Jr. on 2022-04-28, “The Man Who Changed the Earth’s Atmosphere—for the Worse”.


Aviation is a highly risk averse industry. Human flight is a credit to pilots and mechanics today and manufacturers and engineers from decades ago.

Perhaps in the not too distant future, SpaceX Starship rockets cryogenic methane combustion will leapfrog aviation (no lead, or even pesky carbonization here). But likely general aviation will continue as is for training for hundreds of years more.

Speaking of working museums, during my inspections for a company replacing furnaces in the 1990s, I witnessed working coal furnaces from the late1800s in public schools. The public (i.e. government) schools had permission from the City to ignore “blue sky” laws.

Not all janitors were diligent, but a diligent one had such a clean operation, I felt like I was stepped back to the late 1800’s, and witnessed in 1996, a working centrifugal spinning ball governor (aka Watt Governor)! We humans can maintain things for a long, long time if compensated for our efforts!



The FAA, like ALL bureaucracies, is an empire-building affair. Their job is “regulating”, and there is never enough regulations.

Take the Class III physical requirements. I am having to jump through hoops to get my medical back - because i am a very well regulated diabetic. Now, the license would only allow me to fly - and take any who are willing to go with me, in the airplane. No flying for hire OR compensation, where the traveler probably doesn’t know anything about the pilot. In practical terms this means I can fly a twin of some 600 total HP, generally in highly regulated airspace. BUT I can drive my Vette every day without all the rigamarole, and IT has 650 HP, and I drive in generally highly congested spaces, especially when viewing flying.

?So why the difference. Bureaucracy. They have long constructed a system of “control” that gives them power and “relevancy”. It is only recently that they have even allowed diabetics to fly. Oh, horrors! Someone who has been using insulin for over 18 years, has not had a significant drop in more than 10 years, has great labs, is enthusiastically viewed by his endocrinologist - isn’t “safe” to fly. And I don’t need any of that to drive, just a statement from my doc that I am good to go. I call BS.