Textron Cessna 172R, Pilot Operating Handbook, Page: 289 / 500

CESSNA
MODEL 172R
SECTION
8
HANDLING, SERVICE
&
MAINTENANCE
One exception
to
this can be encountered when
operating under
rthe combined effect of: (1) use of certain
fuels,
with
(2)
high
humidity conditions on the
ground (3) followed by flight at high
altitude and low
temperature.
Under these unusual
conditions, small
amounts of water
in solution can
precipitate from the fuel
stream
and
freeze
in
sufficient quantities to induce partial icing of
the
engine fuel
system.
While these
conditions are quite rare and will
not normally pose
a
problem
to
owners and
operators, they do exist in certain areas
of
the world and consequently
must be dealt with, when encountered.
Therefore, to help alleviate the
possibility of fuel icing occurring
under these unusual conditions,
it is permissible to add isopropyl
alcohol or diethylene glycol monomethyl
ether (DiEGME) compound
to
the
fuel supply.
The introduction of alcohol or DiEGME
compound into the fuel
provides
two
distinct effects: (1) it absorbs the dissolved
water
from
the gasoline and (2) alcohol has a
freezing temperature depressant
effect.
NOTE
When using fuel additives, it must
be remembered that the
final goal is
to
obtain a
correct fuel-to-additive ratio in the
tank, and
not
just with
fuel coming
out
of the
refueling
nozzle. For example,
adding 15 gallons of correctly
proportioned fuel
to a tank which contains
20
gallons of
untreated
fuel will result in a lower-than-acceptable
concentration level
to the 35 gallons of fuel which now
reside in the tank.
Alcohol, if used, is
to
be blended
with the fuel in a concentration
of
1%
by volume. Concentrations
greater than 1% are
not
recommended since they can be detrimental
to fuel tank materials.
The manner in which
the alcohol is added
to
the
fuel is
significant because alcohol is
most effective when it is completely
i#*' dissolved in the fuel. To ensure proper mixing, the
following is
recommended:
1.
For best
results, the alcohol should be added during
the
fueling
operation by pouring the alcohol
directly on the
fuel
stream
issuing from the fueling nozzle.
Feb
28/00
8-17
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