Fuel Indicating System - Cessna 172S NAV III Pilot Operating Handbook

SECTION 7
AIRPLANE AND SYSTEMS DESCRIPTION
FUEL SYSTEM
(Continued)
FUEL INDICATING SYSTEM
CESSNA
MODEL 172S NAV III
Fuel quantity is measured by two float-type fuel quantity sensors
(one in each tank) and is displayed on all Engine Indicating System
(EIS) pages. The indicators are marked in gallons of fuel. An
empty tank is displayed on the fuel quantity indicator (FUEL QTY
GAL) as a red line on the far left of the indicator scale, and the
number "0". When an indicator shows an empty tank, approximately
1.5 gallons of unusable fuel remain in the tank. The indicators
should not be relied upon for accurate readings during skids, slips
or unusual attitudes.
The fuel quantity indicator shows the fuel available in the tank up to
the limit of the sensor float travel. At this level, additional fuel may
be added to completely fill the tank, but no additional movement of
the float or the indicator will result. The limit for sensor float travel
is approximately 24 gallons and is indicated by the maximum limit
of the green arc. When the fuel level decreases below maximum
travel of the fuel sensor, the fuel quantity indicator will display fuel
quantity measured in each tank. A visual check of each wing tank
fuel level must be performed prior to each flight. Compare the
visual fuel level and indicated fuel quantity to accurately estimate
usable fuel.
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 tank
pointers are in the yellow arc range and/or any LOW
FUEL annunciator is on.
(Continued Next Page)
7-38
U.S.
172SPHAUS-00