Textron Cessna C172S PIM, Pilot Operating Handbook

Page: 254 / 322

SECTION 7 CESSNA
AIRPLANE AND SYSTEM DESCRIPTION MODEL 172S NAV III
GFC 700 AFCS
U.S.
FUEL SYSTEM
(Continued)
FUEL INDICATING SYSTEM
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The fuel quantity indicators detect low fuel conditions and incorrect
sensor outputs. When fuel quantity is less than 5 gallons indicated (and
remains less than this level for more than 60 seconds), LOW FUEL L
(left) and/or LOW FUEL R (right) will be displayed in amber on the PFD
and a tone will sound. The fuel quantity indicator pointer(s) and
indicator label will change from white to steady amber. When fuel
quantity reaches the calibrated usable fuel empty level, the LOW FUEL
L and/or LOW FUEL R remain amber and the indicator pointer(s) and
label change to flashing red.
NOTE
Takeoff is not recommended if both fuel quantity indicator
pointers are in the yellow band range and/or amber LOW
FUEL L or LOW FUEL R annunciator is displayed on the
PFD.
In addition to low fuel annunciation, the warning logic is designed to
report failures with each sensor. If the system detects a failure, the
affected fuel indicator will display a red X. A red X through the top part
of the indicator indicates a failure associated with the left fuel tank. A
red X through the bottom part of the indicator indicates a failure
associated with the right fuel tank.
Fuel flow is measured by use of a turbine type transducer mounted on
top of the engine between the fuel/air control unit and the fuel
distribution unit. This flow meter produces a signal that is displayed as
the rate of fuel flow on the FFLOW GPH indicator on the EIS pages.
FFLOW GPH is shown as either a horizontal analog indicator or a
digital value, depending on the active EIS page.
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172SPHBUS-00
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