Cessna 172R, Operating Handbook

Page: 90 / 500

SECTION
3
EMERGENCY PROCEDURES
CESSNA
MODEL 172R
ROUGH ENGINE OPERATION
OR LOSS
OF
POWER
SPARK PLUG 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
mixture
to
the recommended lean setting for cruising flight. If the
problem does
not
clear up in several minutes, determine if a richer
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 magneto is malfunctioning. Select
different power settings and enrichen the mixture to
determine
if
Icontinued
operation
on
BOTH magnetos
is possible. If
not,
switch
to
the good magneto
and proceed
to
the
nearest
airport
for
repairs.
ENGINE-DRIVEN FUEL
PUMP FAILURE
Failure of the engine-driven fuel
pump will
result in an immediate
loss of engine
power, similar
to
fuel exhaustion
or
starvation, but
while
operating from a fuel tank containing adequate fuel. A sudden
reduction in indicated fuel flow will
occur just before loss of engine
power.
If the engine-driven fuel
pump fails, immediately
set
the auxiliary
fuel
pump switch (FUEL PUMP) to the ON
position
to restore
engine
power. The flight should be
terminated as soon as practical and the
engine-driven fuel pump repaired.
3-20
Revision 7