Cessna 172N - Page 38

SECTION
3
EMERGENCY
PR,OCEDURES
CESSNA
MODEL 172N
ROUGH ENGINE
OPERATION OR
LOSS OF POWER
CARBURETOR
ICING
A
gradual
loss of
RPM
and evenhral engine
roughness
may result from
the
formation of carbruretor
ice. To
clear
the ice,
apply
full throttle
and
pull
the carburetor heat
knob
fulI out
until the engine
runs
smoothly;
then
remove
carburetor
heat and readjust the throttle. If
conditions require
the
continued use of
carburetor
heat
in
cnrise
flight, use the minimum
amount of heat
necessary to
prevent
ice from
forming
and
lean the
mix-
ture for
smoothest engine
operation.
SPARK
PtUG
FOULING
A
slight
engine
roughness
in flight may be caused
by one or
more
spark
plugs
becoming
fouled
by
carbon or lead
deposits.
This
may
be
verified by
turning
the
ignition
switch
momentarily
from BOTH
to either
L or
R
position.
An obvious
power
loss in
single
ignition operation is
evidence
of
spark
plug
or
magneto
trouble.
Assuming
that
spark
plugs
are the
more
likely
cause,
lean
the
mixbure to
the
recommended lean
set-
ting
for
cruising
flight.
If the
problem
does not
clear up
in
several
min-
utes,
determine
if a
richer
mixh.rre
setting
will
produce
smoother
opera-
tion.
If
not,
proceed
to
the
nearest airport for repairs
using
the BOTH
position
of
the
ignition
switch unless extreme roughness
dictates
the use
of a
single ignition
position.
TVI
AG N ETO'VT
A IFU NCTION
A
sudden
engine
roughness
or
misfiring
is usually evidence
of mag-
neto
problems.
Switching from
BOTH to either L
or R ignition
switch
position
will identify
which magneto
is maUunctioning.
Select different
power
settings
and
enrichen the
mixture
to
determine
if continued
opera-
tion on
BOTH magnetos
is
practicable.
If not,
switch to the
good
magneto
and
proceed
to the
nearest airport
for
repairs.
LOW
OIT
PRESSURE
If low
oil
pressure
is accompanied
by
normal
oil
temperature,
there
is
a
possibility
the
oil
pressure
gage
or
relief valve
is
maLfunctioning.
A
leak in
the
line
to
the
gage
is
not necessarily
cause
for
an
immediate
pre-
cautionary
landing
because
an
orifice
in
this
line
will
prevent
a
sudden
loss of oil from the
engine
sump.
However,
a
landing at the
nearest
air-
port
would be advisable
to
inspect
the
source
of trouble.
If a total
loss of
oil
pressure
i:s
accompanied
by
a rise
in
oil temper-
ature, there
is
good
reason
to suspect an engine
failure
is imminent.
Re-
3-
14