The vast majority of the U.S. general aviation fleet burns gasoline. Yet, the continued supply of avgas is by no means assured: Its continued widespread availability hinges on the outcome of future challenges from environmentalists and the supply of additives, among other factors. AVweb contributor Paul Merritt examines these issues and takes a look at what's going on in the industry to address them and develop alternatives.
November 29, 2000
it would be easier to just bury our heads in the sand and ignore the coming
aviation-gasoline crisis. This is what I believe most of us in aviation are
doing. I am referring to the possibility of the demise of both the aviation
and auto gasoline that we currently use in our aircraft. The causes of this
potential crisis go back more than 30 years, when the government told the
transportation community to "get the lead out." Most of the
transportation business took this command seriously and have long since done
away with lead in their fuel, but we in aviation made one immediate change and
then went to sleep.
A Brief History Of Time
The one change we made was to switch to a new gasoline called 100 Low Lead
or 100LL. Sold as a replacement for both the 100-octane and 80-octane fuels
available at that time, the new 100LL only contained half the lead of the old
100-octane; however, it contained four times the lead of the old 80-octane. In
spite of its lead content, it was sold as a contribution to the environment.
In reality, its use did not benefit the environment much but rather benefited
the aviation-fuel industry, enabling it to reduce the number of products it
had to produce, distribute, stock and sell. Also, since most airports at the
time had only two fuel systems, the airports were able to switch from selling
two grades of gasoline to selling only one grade, utilizing the second tank
and pump to sell jet fuel.
However, as the lower compression engines really did not run so well on the
new "marvel" fuel called 100LL (because of the amount of lead it
still contained: four times as much as the old 80-octane), it wasn't long
before the aviation community began to seriously look at using automobile gas
in the lower-compression engines that didn't need 100-octane fuel. As a
result, in spite of many experts proclaiming the sky would fall if we operated
on auto gas, its
use was subsequently approved in 1982, and this fuel has proven to be a
safe way to rid lower-compression engines of the ravages of the heavy amount
of lead in 100LL.
Afterwards, for almost 20 years, we saw relative peace in the world of
gasoline for airplanes. There was a blip a few years ago when Congress and the
EPA decided we needed an oxygenation agent in our auto gasoline sold in
cities. Fortunately for the aviation industry, the chemical compound that was
decided upon as an oxygenation agent for most of the fuel sold was MTBE
(methyl tertiary butyl ether). Since MTBE was "approved" for
aviation usage, we were able to keep using the reformulated car-gas as long as
it contained MTBE, not the other oxygenation agent, ethanol.
The Coming Challenges
those years of peace are apparently coming to an end, and we are facing a
potential gas crisis. The first cause of this possible crisis is MTBE, which
has proven to be quite a polluter and is showing up in our water supply. Thus,
the government will probably be forced to either eliminate the use of an
oxygenation agent altogether or require the use of ethanol as the only
oxygenation agent. Using ethanol would essentially void all of our permits to
use auto fuel in our aircraft. We would either have to use 100LL as long as it
is available (and cope with its lead-fouling, etc.), or try to find a source
for auto fuel without the ethanol.
Another factor in the developing crisis is that the EPA must eventually
force aviation to comply with the same regulations concerning lead in fuel as
everyone else. Although the EPA has let aviation skate along and use lead in
its gas for more than thirty years, who knows how much longer this situation
will continue. The optimist will say ten years; the pessimist will say one.
Actually, aviation has greatly reduced its total use of lead over the last
thirty years, since much of commercial aviation and all of military aviation
in this country have switched to turbine engines that burn jet fuel.
However, it may not be regulation but lack of supply that creates a true
crisis and ends our use of lead. Tetraethyl lead is no longer made in the U.S.
A single plant in England makes the lead we use in our 100LL in this country.
Since the demand for tetraethyl lead is steadily decreasing (at a rate of some
15 percent a year), no one knows how much longer lead will be available for
our 100LL. Rumor has it that this supplier is plagued with the difficulties of
compliance with U.K. regulations, so who knows when they will decide
"Enough is enough already!" This plant may simply stop making
tetraethyl, their government may stop them from making it, or our government
may stop us from using lead in our aviation gasoline. In any case, the gas we
need will be gone, and then what will we do?
Before I make suggestions about possible solutions, let me explain why
there was not a solution to the problem when the transportation industry was
first told to "get the lead out." At this time, the aviation
manufacturers had complete confidence that the petroleum industry would pull
off a miracle and come up with a 100-octane fuel that didn't use lead. Thus,
the industry kept making planes that must have 100-octane fuel and it
continues to do so today.
Actually, the petroleum companies worked very hard to try and pull off that
"miracle." I have heard that over 40,000 different compounds were
experimented with in the attempt to replace lead. Some of those compounds
proved successful in increasing the octane but at the same time caused other
problems, such as causing corrosion or proving to be more toxic than lead.
Still, this effort continued for a couple of decades.
Eventually, the demand for aviation gasoline was mostly supplanted by the
demand for jet fuel, and the oil companies gave up on a replacement for 100LL.
The engine and airframe manufacturers knew the oil companies were no longer
attempting to replace the lead a few years back, but most of us plane owners
and operators did not. These manufactures did not publicize this fact. I can
understand the silence. I doubt I'd tell anyone I made a product that needed a
fuel that was going the way of the dinosaurs.
Now to the question, "What can we do?" First, let's look at those
solutions that have been proposed. Each has its problems. One easy solution
would be to produce and distribute a 92-octane aviation fuel which would be
"good enough" for some of the engines that we currently think of as
100-octane engines. Why 92-octane? Well, that seems about the best we can hope
for without lead.
your engine won't run on 92-octane, an obvious solution would be to make
modifications that would enable it to run on "92." The old standby
way to cope with lower octane fuel is to lower the compression ratio. This
change in ratio could be done, but it in turn would create new problems. It
would not only cost a lot of money, but the power output of the engine would
be reduced, which would necessitate re-certification of each make and model of
aircraft by the FAA. Thus, you would have the problem of the paperwork
required for re-certification and the cost of the STC.
...Electronic Ignition And Injection Systems...
Another possible solution is to replace our antiquated magnetos and fuel
injection systems with modern electronic ones. The engine manufacturers are
busy working on such systems. I find my experience with one of those
manufacturers, Teledyne Continental Motors (TCM), and its denial that there
was a problem with their engines (related to fuel) both comical and revealing.
When TCM first displayed their new ignition/injection system, I asked their
representatives if they were developing it for the purpose of coping with
unleaded fuel. They vehemently denied that was the case, but this year at EAA
AirVenture, they began to admit that this is the main purpose for the system.
The TCM people knew there was a coming fuel crisis, which would make the
engines they were manufacturing obsolete. However, they wanted everyone to
keep buying their "short-lived" engines; then when the crisis
arrived, they could announce they had a "solution" to sell to the
Experts disagree on whether such a system will be enough to allow all
engines to work on 92-octane fuel. A good guess is that some will and some
won't. The particularly high-output engines probably won't make it, and the
ones with carburetors probably won't be helped much. Good questions to ponder
on this subject are "Will my particular make and model be included in the
solutions?" and "What will the cost be?" I'd guess you had
better set aside $5,000 to $10,000 for any engine modifications that would
allow you to run on 92-octane.
course, all the above assumes there will be a 92-octane aviation fuel in our
future. When the lead is gone, maybe the oil companies won't bother, and our
airports will have just one fuel available: jet fuel. I've already run across
several such airports. Switching to an engine that burns jet fuel, of course,
is the ultimate fix. It would be nice if we all had turbine engines, but since
these conversions currently cost in the range of $500,000, this obviously is
not the fix for most of us. Meanwhile, the engine manufacturers are looking at
another solution, using diesels rather than turbines to replace our existing
These diesels would cost a lot less than turbines and would run on the jet
fuel available everywhere. Hopefully, they would simply bolt on to our
existing airframes without a lot of modification. Aviators had hoped to see
some of these diesel engines flying this year at EAA AirVenture 2000. They
were not there, and there were rumors that these diesels have lots of
Of course, again, you had better hope you have an engine and airframe that
is a popular model, as probably nobody will go to the expense of certifying a
diesel for the less-popular models. Also, these engines will not be cheap. I'd
guess it would cost you somewhere between $40,000 and $75,000 to convert your
little single to a diesel. However, speculating on the cost is again
"jumping the gun," because someone must first get one certified.
In The Meantime...
So, what can we do just now? If you are rich, you could avoid all of these
problems by selling your gasoline-burning planes right away (before others
read this article) and buy a jet, or you could convert your existing plane to
a turbine, if such a conversion is available. If you are poor and currently
fly on car gas, you could call your congressperson and ask him/her to work to
make sure you continue to have available gas that does not have ethanol in it.
you are middle-class and own a bird that can only run on 100-octane, you
should probably fly a lot, while you can still get 100LL, and pray that some
bright engineer comes up with an inexpensive way to make your engine cope with
a lower octane fuel or a way to make a 100-octane substitute without lead.
One such possible bright spot may be an ethanol-based fuel shown at EAA
AirVenture this year. It is called AGE85 and was developed under the guidance
of South Dakota State University. The fuel is about 85 percent pure ethanol
made from corn. The other ingredients and proportions are 14 percent pentane
isomerate taken from petroleum and 1 percent biodiesel made from soybeans. The
pentane is added to the ethanol to get the vapor pressure up to acceptable
levels, and the biodiesel prevents corrosion. Already AGE85 is certified for
use on Cessna 180s (with certain modifications), and the developers of this
fuel are currently testing it in a Mooney 201.
Wouldn't it be ironic if the ethanol that could spoil auto gas for our use
should wind up being the replacement for our 100LL? Stranger things have
Happy flying, while we still have fuel!