CESSNA
SECTION 3
MODEL 172S NAV III
EMERGENCY PROCEDURES
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 MAGNETOS 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.
Since 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 MAGNETOS
switch unless extreme roughness makes the use of a single
magneto position necessary.
MAGNETO MALFUNCTION
Sudden engine roughness or misfiring is usually a sign of a
magneto problem. Changing the MAGNETOS switch from BOTH to
the L and R switch positions will identify which magneto is
malfunctioning. Select different power settings and enrichen the
mixture to determine if continued operation on BOTH magnetos is
possible. If not, change to the good magneto and continue to the
nearest airport for repairs.
IDLE POWER ENGINE ROUGHNESS
(As Required by AD 2001-06-17, Paragraph (d)(3))
An excessively rich idle fuel flow may cause low speed engine
roughness during flight. During most in-flight low engine speeds
(power off stalls, approach to landing, etc.), the mixture control is
normally in the full-rich position. However, to improve engine
roughness (caused by an improperly adjusted fuel servo) during low
engine speeds while in flight, you should rotate the vernier mixture
control (leaning of fuel mixture). You may also have to lean the fuel
mixture if this low engine speed results in power loss and you need
to restart the engine during flight. In all cases, you should land the
airplane at the nearest airport for repairs if low speed engine
roughness requires you to adjust the fuel mixture control to improve
engine operation.
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172SPHAUS-01
U.S. 3-31