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ALL ABOUT FUEL
This pamphlet provides information about aviation fuels and the safety
precautions that need to be observed during aircraft fueling.
The introduction of turbine-powered aircraft into the civil
aircraft fleet during the 1950's caused many changes in the marketing
of aircraft fuels. As the air carrier and military fleets were
converted to turbine-powered aircraft, the demand for aviation gasoline
(avgas) decreased drastically. Aviation fuels now represent a
relatively small portion of the petroleum industries by products and
therefore the produKion of avgas in multigrades is no longer
economically feasible. During the past few years, we have seen 91/96,
and 115/145 octane fuels disappear from the market. In 1971 the oil
companies began development of a single grade avgas that would meet the
needs of all reciprocating powered aircraft.
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80/87 vs 100LL
When the 80/87 began to disappear from the avgas market and 100LL was
introduced to take its place, operators expressed concern about the
service life expectancy of their low compression engines. Some
operators experienced accelerated exhaust valve erosion and valve guide
wear from the use of highly leaded 100/130 (green) avgas in their
engines that were rated to use a minimum grade 80 octane fuel. The
engine manufacturers were quick to provide aircraft owners with amended
operating procedures and maintenance schedules which helped minimize
the engine malfunctions resulting from the use of high lead 100/130
avgas. Experience of the past ten years has proven that low compression
aircraft engines can be operated safely on 100 low lead avgas without
difficulty, providing they are operated and serviced in accordance with
the approved aircraft owners manual or other officially approved
document.
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AUTOMOTIVE GASOLINE
Leaded automotive gasoline is not recommended as a substitute for
aviation gasoline because of the differences in properties and
composition of the two types of fuel. Regular leaded automotive
gasoline may cause preignition and detonation, vapor lock, and sticking
or burned valves when used in aircraft engines. Lead-free automotive
gasoline, however, has been extensively tested in aircraft equipped
with low compression engines that use low octane fuel by the
Experimental Aircraft Association and other Organizations. The Federal
Aviation Administration has issued supplemental type certificates (STC)
to these organizations permitting the use of unleaded automotive
gasoline of 87 minimum antiknock index per ASTM specification D-439.
Each make/model aircraft shall be modified and operated in accordance
with the instructions, limitations, and procedures contained in the STC
when unleaded automotive gasoline is used.
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PLACARDS-TYPE OF FUEL
Be sure you get the type of fuel that is specified. Federal regulations
require that all aircraft filler openings must be marked with the word
'fuel' and the minimum fuel grade for reciprocating powered aircraft,
or the permissible fuel designation for turbine-powered aircraft. Even
these requirements do not rule out the possibility of being serviced
with the wrong type of fuel. Pilots should be particularly cautious
when being serviced at facilities that provide turbine fuel as well as
avgas. Turbine or jet fuel is detrimental to the reciprocating engine
and extended use of avgas can damage turbine engines. Therefore, it is
imperative for flight crews to double check when their aircraft is
serviced to assure that they receive the proper type and grade of fuel.
Although this responsibility is placed upon the pilot by regulation it
just makes good sense to be sure. The fuel system sumps should always
be drained and checked for contaminants after each fueling of the
aircraft and during preflight inspection.
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FUEL ADDITIVES
The FAA and several engine manufacturers have approved the use of
certain carburetor anti-icing fuel additives in aviation gasoline.
However, such additives should not be used without consulting the
airframe manufacturer because their chemical content may not be
compatible with the aircraft fuel system cells, seals, etc.
The same is true with lead scavenging additives such as
Tricresyl Phosphate (TCP). TCP, for example, has been used successfully
to reduce lead fouling of spark plugs in normally aspirated
reciprocating engines for several years. However, TCP should not be
used in turbocharged or supercharged engines without approval of the
airframe manufacturer. TCP must be mixed according to the instructions
provided by the manufacturer, Alcor Inc., for maximum effectiveness.
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SPARK PLUG FOULING AND HOW TO AVOID IT
In most cases spark plug fouling can be reduced or eliminated by simply
applying proven operating techniques. For example, low operating
temperatures coupled with rich fuel mixtures result in incomplete
vaporization of the tetraethyl lead in the combustion chamber causing
lead fouling of the spark plugs. Maintaining proper cylinder head
temperatures will minimize plug fouling problems. Be certain that
maintenance personnel have installed the spark plugs recommended for
the particular engine installation. Have the carburetor idle mixture
checked and adjusted. Use recommended leaning techniques in cruise
condition at all altitudes. Avoid low power letdowns, descend with
power, and avoid over rich conditions. Carburetors and fuel injectors
are normally set slightly rich in the closed throttle position, so it
is best to carry a slight amount of power on landing approaches rather
than approach with closed throttle. Keep the cylinder temperatures in
the normal range during operation. After flight or ground operations,
before shutdown, advance the throttle to about 1800 RPM for 15 to 20
seconds to clear the plugs and combustion chambers, retard the throttle
to about 1200 RPM and shut the engine off immediately with the mixture
control. You should not have plug fouling or misfiring on your next
startup. As long as you make sure the aircraft is serviced with the
proper fuel, check the sumps for contaminants, operate the engine
according to the aircraft owners manual and have the spark plugs
serviced as recommended, you should not have plug fouling problems.
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TURBINE FUEL
Occasionally, aircraft are inadvertently serviced with the wrong type
of fuel and in most instances it is because of misleading signs. For
example, certain turbo-supercharged reciprocating powered aircraft have
paint designs with the word TURBO conspicuously displayed on the
vertical stabilizer or on the engine nacelle. Line service personnel
assumed this to mean turbojet and filled the tanks with jet fuel.
Another incident involved an air carrier type aircraft that was
originally equipped with reciprocating engines which most operators
converted to turbo-props. The service personnel assumed the aircraft
was a converted model when it wasn't.
Reciprocating engines may run briefly on jet fuel, but
detonation and overheating will soon cause power failure. So, beware of
getting jet fuel when you need avgas. Avgas is no substitute for jet
fuel either. The engine failure caused by running the turbine engine on
the wrong fuel may not be as sudden, but prolonged operation on
gasoline will severely damage the engine by the lead content and
differiny combustion ranges of the fuel. Time limitations for use of
avgas in turbine engines are listed in the airplane or rotorcraft
flight manual.
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PRE-FLIGHT ACTION
The responsibility is yours, the pilot, to determine that your aircraft
is properly serviced. Check your aircraft before each flight and be
sure yu have the correct type of fuel. It may save your life. Take the
time to inspect your aircraft thoroughly. (1) Be sure all of the fuel
and oil tank caps and covers are installed and secured properly after
you visually check the fluid level. Observe the color and odor of the
fuel as you check the tank. (2) Draw a generous sample of fuel from
each sump and screen drain into a transparent container. Check for the
presence of water, dirt, rust or other contaminants. Don't be so frugal
as to save the fuel drained from the sumps by pouring it back into the
tank. There are people who do. Don't risk the possibility of
contaminating the system, get rid of it. (3) Check that each fuel tank
vent is clear of restrictions; i.e., dirt, ice, snow, bent or pinched
tubes, etc.
(END OF DOCUMENT FAA-P-8740-35A
AFO-800-09-83)
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