Textron Cessna 172S Skyhawk SP, Information Manual

Page: 185 / 491

SECTION 7
AIRPLANE
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SYSTt:MS DESCRIPTION
FUEL VENTING
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, ,CESSNA
MODEL 172S
Fuel system venting is essential to ,system operation, Blockage'
'of the system will result in decreasing fuel flow and eventual engine
stoppage, Venting is' accomplished by an interconnecting :Iine from
the right fuel tank to the left ..tank. The. left, fuel tank is vented'
overboard through a vent line, equipped with a check valve, which
protrudes from the bottom surface of' the, left wing near the wing
strut. Both fuel filler caps are also vented..
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REDUCED TANK CAPACITY
The airplane may' be serviced to a reduced capacity to permit
heavier cabin loadings. This is accomplished by'filling each tank to
the bottom .edge of the fuel filler tab, thus giving a reduced fuel load
of 17.5 gallons usable in each tank. '
FUEL SELECTOR VALVE
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The fuel selector valve should be' in 'the 'BOTH position for
takeoff, climb, landing, and maneuvers that involve prolonged slips
or skids of more than, 30 seconds. Operation from either LEFT or
RIGHT tank 'is reserved for cruising flight.
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NOTE
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, When the fuel selector valve handle is.in the Bon-i position,
in cruising flight, unequal fuel flow from each tank may.
occur if the wings are not. maintained exactly ,level.
Resulting, wing, heaviness can be: alleviated graduaIlY,.by'
turning the selector valve handle to the tank in the "h,eavy".
wing:
It is not practical to measure the time required to'
consume all of the fuel in one tank, and, after switching to
the opposite tank, expecf' an ,equal' duration, .from' ,the
remaining ,fuel. The airspace in', both fuel tanks' is
interconnected by a vent line and,' therefOre, some sloshing
of fuel between tanks can be expected when the tanks are'
nearly full and the wings are not level.
7-26
'July 8/98