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Category Archives: COPA Flight Magazine

Aviation Fuel – MOGAS, 100LL, and Beyond

Fuel pumps at Brockville – 1000 Islands Tackaberry Regional Airport (CNL3)
Fuel pumps at Brockville – 1000 Islands Tackaberry Regional Airport (CNL3)
Fuel pumps at Brockville – 1000 Islands Tackaberry Regional Airport (CNL3)

Written by: George Farrington, Director, External Relations

For many pilots, MOGAS or motor gasoline presents a cost effective and easy to come by fuel
option. There are even some aircraft engines, such as the Rotax 900 series of engines, where
MOGAS is suggested for use over AVGAS (aviation gasoline). Dozens of aircraft engines and
hundreds of certified airframes can also apply for a MOGAS Supplemental Type Certificate (STC),
which permits the use of MOGAS in that aircraft.

MOGAS STCs have existed since the 80s, and can provide a cost benefit, an easier to access fuel
source and potentially reduced maintenance requirements. With a lot of older aircraft piston
engines originally designed to operate on fuel octanes lower than current automotive fuel, the
STC is usually a paperwork endeavour, with a handy sticker to demonstrate that the aircraft is
approved for MOGAS use.

Canada’s Clean Fuel Regulations, which came into effect in July 2023, encourages the use of
clean fuels like ethanol to be blended automotive gasoline and some provinces and territories
require the addition of 5 to 10% ethanol to gasoline.

Groups are protesting the lack of ethanol free fuel, as current gasoline containing ethanol can
have adverse effects on classic cars, small gasoline engines and marine engines. The engines
and fuel systems of most modern vehicles are not affected by fuel containing ethanol, however
there are many vehicles that are adversely affected by the use of ethanol. The most recent
petition to the Government of Canada initiated by an individual on behalf of vintage
automobile owners in Canada is requesting ethanol free fuel be available in higher octanes,
able to be purchased at automotive fuel stations.

When used in some aircraft, ethanol can degrade certain plastics, fibreglass, rubbers and
aluminum that form part of the fuel system of many aircraft, and aircraft accidents have
occurred from blocked fuel filters and lines from the degraded tanks and hoses. Additionally,
ethanol can absorb a larger amount of water than gasoline can, so any condensation or other
water in the fuel tank will be absorbed at a higher rate, with the potential to cause issues with
combustion and effect fuel flow.

Ethanol can cause vapour lock, which can cause engine fuel starvation. This is especially
prevalent at altitude, and some aviation authorities have prohibited the use of MOGAS above a
set altitude, in the case of the UK Light Aircraft Association 6000ft. Additionally, the greater
volatility of MOGAS compared to AVGAS means that the carburettor throat temperatures are
lowered more by the atomisation of MOGAS at the jet than occurs with AVGAS, which can
make a carburetor more susceptible to icing when using MOGAS.

Some engines are approved for a certain percentage of ethanol, some as high as 10%, however
for ethanol to be used the fuel system needs to be able to withstand the degrading effects ofethanol, and an aircraft manufacturer will specify the ethanol content that can be used in the
aircraft. While some aviation authorities permit the use of some ethanol, mostly only 5%,
Transport Canada prohibits the use of any ethanol in aircraft, and most MOGAS STCs are
invalidated with the use of ethanol.

The lead found in AVGAS can also cause its own problems, such as fouled spark plugs and
sticking valves, which has led some aircraft owners to mix AVGAS with MOGAS in an effort to
reduce ongoing maintenance costs.

Lead itself also presents health and environment issues, and in February 2022 the Eliminate
Aviation Gas Lead Emissions (or EAGLE) group was set up by general aviation trade associations
and the US Federal Aviation Administration (FAA), with the goal of transitioning to lead free fuel
by 2030. This was additionally motivated by findings from the US Environmental Protection
Agency (EPA), which in October 2023 announced its final determination that emissions of lead
from aircraft that operate on leaded fuel cause or contribute to air pollution which may
reasonably be anticipated to endanger public health and welfare.

Unleaded aviation fuels such as UL91 are already in use around the world however these are
not compatible with all general aviation engines. The aim of EAGLE is to identify a “drop in”
high octane replacement for 100LL AVGAS, to allow a seamless transition to the new fuel type.
COPA is a contributor to EAGLE meetings, bringing a Canadian GA perspective, and monitors
progression in the development of fuel to ensure that its members and the GA community are
aware of potential future fuel availability in Canada.

As work is being undertaken to investigate fuel alternatives for traditional piston engines,
research is taking place on further alternative propulsion systems for light aircraft. In the short
term, Sustainable Aviation Fuels (SAF) are showing promising results after both short tests and
trans-Atlantic flights, many electric aircraft are in development with one certified, and
hydrogen is being researched as a future aviation fuel source. While gasoline and piston engine
technology may be the “hot topic” of today, we are on the cusp of new developments in
aviation propulsion.