Textron Aviation Cessna 172S NAV III Skyhawk SP, Information Manual

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CESSNA SECTION 7
MODEL 172S NAV III AIRPLANE AND SYSTEM DESCRIPTION
KAP 140 AUTOPILOT
U.S.
FUEL SYSTEM
(Continued)
AUXILIARY FUEL PUMP OPERATION
The auxiliary fuel pump is used primarily for priming the engine before
starting. Priming is accomplished through the fuel injection system. The
engine may be flooded if the auxiliary FUEL PUMP switch is
accidentally placed in the ON position for prolonged periods, with
MASTER Switch ON and mixture rich, with the engine stopped.
The auxiliary fuel pump is also used for vapor suppression in hot
weather. Normally, momentary use will be sufficient for vapor
suppression; however, continuous operation is permissible if required.
Turning on the auxiliary fuel pump with a normally operating engine-
driven fuel pump will result in only a very minor enrichment of the
mixture.
It is not necessary to operate the auxiliary fuel pump during normal
takeoff and landing, since gravity and the engine-driven fuel pump will
supply adequate fuel flow. In the event of failure of the engine-driven
fuel pump, use of the auxiliary fuel pump will provide sufficient fuel to
maintain flight at maximum continuous power.
Under hot day, high altitude conditions, or conditions during a climb that
are conducive to fuel vapor formation, it may be necessary to utilize the
auxiliary fuel pump to attain or stabilize the fuel flow required for the
type of climb being performed. In this case, turn the auxiliary fuel pump
on, and adjust the mixture to the desired fuel flow. If fluctuating fuel flow
(greater than 1 GPH) is observed during climb or cruise at high
altitudes on hot days, place the auxiliary fuel pump switch in the ON
position to clear the fuel system of vapor. The auxiliary fuel pump may
be operated continuously in cruise.
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172SPHAUS-05 7-43
For
Training
Purposes
Only