BAL scientists engineer yeast to produce ethanol from brown seaweed; brown seaweed biorefinery
Tata Motors commits almost $50M to UK National Automotive Innovation Campus

Shell develops lead-free aviation gasoline

Shell has developed a lead-free replacement for aviation gasoline (Avgas 100 and 100LL); the replacement fuel will now begin a strict regulatory approvals process. Shell is the first major oil company to do so. The new lead-free formulation comes after 10 years of R&D, as well as successful initial testing, carried out in the last two months by two original equipment manufacturers (OEMs).

Avgas is one of the last common transportation fuels—and the only fuel in the US—to contain the additive tetraethyl lead (TEL); avgas is used by light aircraft and helicopters. (Leaded gasoline for automobiles was phased out of use in the US by 1995 due to its environmental and health impact.) Avgas includes lead in its formulation to meet fuel specifications, to boost combustion performance, and to prevent knock.

Aviation fuels
There are two main types of aviation fuel: aviation turbine fuel (jet fuel) and aviation gasoline (Avgas). Jet fuel is used by larger, gas-turbine-engine powered aircraft, while Avgas is used in smaller, piston-engine powered aircraft.
There are currently two main Avgas grades, 100 and 100LL (low lead). 100 is a measurement of octane rating. There are specialty grades at the low-and high end: Avgas 80/87 for low-compression-ratio engines with little or no lead, and Avgas 115/145 for high performance piston aircraft engines used in World War II and the Korean conflict. The latter is very hard to find, and is usually only produced on special order.
Lead emissions from piston-engine aircraft operating on leaded fuel are currently the largest source of Pb air emissions on a national scale, according to the US Environmental Protection Agency (EPA).
Avgas 100LL, the most commonly used avgas, can contain up to 2.12 grams Pb per gallon (ASTM D 910). The Federal Aviation Administration estimates that in 2008, 248 million gallons of avgas were consumed in the US, contributing an estimated 550 tons of Pb to the air that comprise 57% of the national Pb inventory.
Leaded avgas is used at approximately 20,000 airport facilities in the US.

Shell says that its unleaded Avgas meets all key Avgas properties and has a Motor Octane rating of more than 100, an industry standard.

The development of a technically and commercially-viable unleaded Avgas that meets these criteria has been seen by the aviation industry as a significant challenge, due to the tight specifications and strict flight safety standards to which it must adhere.

To get to this stage, Shell Aviation technologists carried out an intensive internal laboratory program, including in-house altitude rig and engine testing. Working alliances were then formed with aviation engine manufacturer Lycoming Engines (Lycoming) and the light aircraft manufacturer Piper Aircraft Inc. (Piper). As a result, the formulation was successfully evaluated in industry laboratory engine (bench) tests by Lycoming and in a flight test by Piper.

Lycoming Engines commends Shell on launching its unleaded Avgas initiative. They engaged Lycoming to test their fuel on our highest octane demand engine and we can confirm that it’s remarkably close to Avgas 100LL from a performance perspective. This initiative is a major step in the right direction for general aviation.

—Michael Kraft, Senior Vice-President and General Manager of Lycoming Engines

Piper Aircraft is pleased to participate with Shell and Lycoming in this feasibility flight test program. Recently, we successfully flew an experimental non-production Piper Saratoga with Shell’s new formulation for about an hour. We appreciate the opportunity to work with Shell and Lycoming in this preliminary investigation of the technologies, which could in several years lead to flying unleaded fuel in our production airplanes.

—Piper Vice-President of Engineering Jack Mill

Shell will now engage the aviation industry, regulators and authorities, including the US Federal Aviation Administration, American Society for Testing and Materials (ASTM) and European Aviation Safety Agency (EASA) to achieve approvals for the unleaded Avgas. Shell expects to also work with other OEMs to continue the testing and refinement program as the approvals process progresses.

Regulatory issues. Globally, petitions and potential litigation from environmental organizations are pushing regulatory agencies to consider actions to eliminate or reduce lead emissions from aircraft.

In the US, the EPA began gathering data in 2010 prior to a presumed rulemaking on lead emissions from piston-engine aircraft using leaded aviation gasoline (avgas). (Earlier post.)

The timeline for completion of this investigation and possible issuance of a final endangerment determination includes completion of necessary modeling and monitoring information and other data, development of a proposal which will be published for public comment, review and analysis of comments received and issuance of the final determination.

If the EPA issues a positive determination that lead emissions from aircraft engines cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare, the EPA would then be required to propose and promulgate emissions standards to control aircraft engine lead emissions, and the Federal Aviation Administration would be required to promulgate regulations addressing the fuel.

In a 2012 report on unleaded avgas, the Federal Aviation Administration (FAA) noted that worldwide uncertainty and concern exists amongst piston aircraft equipment manufacturers, avgas producers, avgas distributors, fixed base operators, aircraft owners and aircraft operators regarding: future utility and value of existing aircraft; availability and cost of aviation gasoline to maintain viable business operations; (c) justification of new aviation product development; and (d) justification of new aircraft purchases.




About bloody time.
There is no known lower limit to the amount of lead which causes damage, and the oil companies were not pushed hard enough by regulation to devote th3e resources needed to eliminate this lethal contamination.


I once read that a Cessna 182 with full tanks of 100 octane (dyed green, not 100 LL, low-lead, which is dyed blue) carried roughly a pound of elemental lead in the fuel.  In all fairness, other routes of exposure probably account for far more human lead exposure to the general public, and almost all of the risk to children.

If this no-lead formulation is compatible with all the materials in the aircraft fleet, it is a very good thing to have.  The one thing I'd worry about is scarcity; if FBOs cannot get a reliable supply, it's worse than useless.

I'm surprised that direct LPG injection hasn't made it to aircraft yet.  It seems it would be far more widely available than avgas, has higher octane, no lead, and eliminates issues of vapor lock due to the sealed fuel system.


The biggest source of lead contamination is the old paint etc, but my understanding is that downwind of airports the emissions can be high enough to be of concern, especially as there does not seem to be a lower dosage limit to damage.


Have there been any studies of people who live and work downwind of small airports (where most of the aircraft would be recips, not turbines) which show elevated blood lead levels?


I didn't keep my references on this, but pretty much, yup.
A quick google yields:

'Testing on how that effects surrounding neighborhoods is relatively new. Two of the first investigations — conducted by the Southern California Air Quality Management District at the Santa Monica and Van Nuys airports in the spring of 2006 and winter of 2007 – found lead concentrations near the runways that were five to 10 times higher than the Los Angeles Basin average. In the neighborhood just east of Santa Monica Airport, concentrations continued to exceed background levels for more than half a mile downwind of the runway.

AQMD spokesman Sam Atwood noted that the pollution never rose above the national safety cutoff, 0.15 micrograms of lead per cubic meter of air. The Los Angeles basin average during the test period was 0.0086 microgram, In Van Nuys, the highest level recorded was 0.0261 and in Santa Monica, 0.096.

Testifying in November at a hearing of the state Senate Select Committee on Air Quality, Hoang said a 2010 study by the EPA found similar results. Soil and dust samples taken on Santa Monica Airport property and at local parks did not show lead levels above the local norm, she said.

Likewise Robert Freeman, environmental manager for Los Angeles World Airports, which runs Van Nuys – the nation’s busiest general-aviation airport – said “We have not seen anything that really alarms us.”

But John Froines, professor emeritus at the UCLA School of Public Health, said there is cause for concern.

At the Select Committee hearing, Froines acknowledged that the Centers for Disease Control sets the safety limit at 10 micrograms per deciliter of blood.

Research shows children can suffer a significant cognitive decline at levels between 1 and 5 micrograms, he said.'

but in my view the limits are too high:

So, it is not a world ending panic, but should in my view be jolly well stopped ASAP

Most aircraft can also run automotive unleaded under a type of certification called an STC. Many require only updated placards and paperwork. Some require minor changes to fuel lines and pumps. The testing and documentation for most of the STCs was developed by Petersen Aviation.

Some aircraft which use the popular Rotax 912 engine, like the Diamond DA-20 A1, are certified from the factory to use automotive unleaded, and in fact it is the preferred fuel. The Rotax is certified to use unleaded fuel with up to 10% ethanol.


So they're finding lead near the hangars, run-up areas, runways etc. (where you'd expect to find it, since it's emitted close to the ground and settles quickly), but nothing showing any real effect on humans.

Lead-free fuel is obviously A Good Thing, but I don't see anything you've cited that would make it urgent.  Recip engines which can operate on autogas or LPG would be a better solution than a new specialty product.


The real problem is with the aircraft engines that are 70 to 80 year old designs. They require high octane fuel not because they are high performance but because they are air-cooled and develop hot spots. Most of the engines are carbureted and even the fuel injected engines use mechanical injected. Typically, you control the head temperatures by controlling the mixture. At higher power, they typically run quite rich so you actually cool the engine by using excess gasoline thru them. What is needed is an aircraft version of a GM turbo direct injection or a Ford Eco-Boost engine.

I am currently building a light sport plane with a Rotax 914 engine which is the turbo-charged version of the 912. While I wish it had electronic direct injection, I consider it far better than than the air-cooled Continental or Lycoming (sometimes referrd to as Lyconsaurus) engines which I would never consider running.


Ah, the days of leaning to 20 degrees lean of peak EGT...

The problem with electronic anything on an aircraft engine is that a failure of a single solder joint can take down the electronic module, which then has to be redundant if it's not to stop the engine and bring down the aircraft.  The whole point of magneto ignition is that if the wire to the ignition switch breaks, it fails operational.

LPG has much higher octane than even avgas, and the charge cooling from direct injection would increase the effective octane even further.  As I said, I wonder why it hasn't gotten anywhere.


Problem with using Mogas (Motorcar gasoline) in present aircraft engines is vapor lock, ethanol, and octane rating. In the days of ethanol free gasoline many operators with low compression engines switched to Mogas. This unfortunately is no longer possible because of the scarcity of ethanol free gasoline. Ethanol deteriorates the materials in the aircraft fuel system. Vapor lock was also a problem because the vapor pressure of Mogas is modified by the refiners from summer to winter.

BTW the total consumption of 100LL by the general aviation fleet is miniscule in comparison the road vehicles.

Incidentally, anything published by the California Air Quality Management District in relation to lead contamination at the Santa Monica and Van Nuys airports is to be taken with a grain of salt. Those folks have had a running battle with the airport users to close the airports for years. The towns want to sell the airport properties to developers thereby increasing tax revenues. These sorts of battles are not unique to California. They are happening all over the country.

People buy homes off the end of runways. Once they have moved in they push to close down the airport. Go figure!

The comments to this entry are closed.