Textron Cessna 172R - Page 289

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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