Cessna 172R, Operating Handbook

Page: 242 / 500

SECTION 7
AIRPLANE
&
SYSTEMS
DESCRIPTION
CESSNA
MODEL 172R
FUEL
VENTING
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 line 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
strut.
Both fuel filler caps
are
also vented.
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
I
the
bottom edge
of
the fuel
filler tab, thus giving a reduced fuel
of
17.5
gallons
usable in each tank.
FUEL
SELECTOR VALVE
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.
_
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
gradually by
turning the selector valve handle
to
the tank in the "heavy"
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, expect
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.
Feb 28/97
NOTE
When
the fuel
selector
valve
handle
is in the BOTH
position