Cessna 172P - Page 46

SECTION
3
EMER,GENCY
PR,OCEDUR,ES
CESSNA
MODEL 172P
ROUGH
ENGINE
OPERATION
OR
LOSS
OF
POWER
CARBURETOR ICING
A
gradual
Ioss of RPM
and eventual engine roughness
may result
from
the forrnation
of carburetor ice. To
clear the ice, apply
full
throttte and
pull
the
oarburetor heat knob full
out until the engine
runs
smoothl$
then
remove
carburetor
heat and readjust
the
throttle. If conditions
require
the
continued use
of carburetor hoat in
cruise flight, use tbe minimum amount
of heat rrecessary
to
prevent
ice from forming
and
lean
the mixture
for
smoothest
engine operation.
SPARK PLUG
FOULING
A
slight engine roughness
in
flight
may be ca,used 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
eithor
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, Iean
the mixture to the recommended lean setting for
cruising
flight, If the
problem
does not
cloar up
in
several
minutes,
determine
if
a
richor
mixture setting will
produce
smoother operation.
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.
MAGNETO MALFUNCTION
A sudden
engine roughness or misfiring is
usually
evidence
of
magneto
problems.
Switching
from BOTH to either L or R ignition switch
position
will identify which ma,gneto is
malfunctioning.
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
OIL
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 ca,use
for an immediate
precau-
tionary
landing
bec&use
a,n
orifice
in this line
wiII
prevent
a
sudden
loss of
oil from the
engine
sump. However, a landing
at
the nearest airport
would
be
advisable to inspect the source of trouble.
If
a total loss
of oil
pressure
is
accompanied
by a rise in oil tempera-
ture, ttrere
is
good
reason to
suspect an engine
failure is imminent. Reduce
3-16
30 May
1980