Textron 172R180HP, Pilot Operating Handbook

Page: 213 / 396

CESSNA
MODEL 172A (180 HP)
FUEL INDICATING
SECTION 7
AIRPLANE & SYSTEMS DESCRIPTION
Fuel quantity is measured by two float type fuel quantity
transmitters (one in each tank) and indicated by an electrically
operated fuel quantity indicator on the left side of the instrument
panel. The gauges are marked in gallons of fuel. An empty tank is
indicated by a red line and the number
o.
When an indicator shows
an empty tank, approximately 1.5 gallons remain in each tank as
unusable fuel. The indicators should not be relied upon for accurate
readings during skids, slips, or unusual attitudes.
Each fuel tank also incorporates warning circuits which can
detect low fuel conditions and erroneous transmitter messages.
Anytime fuel in the tank drops below approximately 5 gallons (and
remains below this level for more than 60 seconds), the amber LOW
FUEL message will flash on the annunciator panel for approximately
10 seconds and then remain steady amber. The annunciator cannot
be turned off by the pilot. If the left tank is low, the message will
read L LOW FUEL. If the right tank is low, the message will read
LOW FUEL R. If both tanks are low, the message will read L LOW
FUEL R.
In addition to low fuel annunciation, the warning circuitry is
designed to report failures with each transmitter caused by shorts,
opens or transmitter resistance which increases over time. If the
circuitry detects any one of these conditions, the fuel level indicator
needle will go to the OFF position (below the o mark on the fuel
indicator), and the amber annunciator will illuminate. If the left tan!<I
transmitter has failed, the message will read L LOW FUEL. If the
right tank transmitter has failed, the message will read LOW FUEL
R. If both tanks transmitters have failed, the message will read L
LOW FUEL R.
Fuel pressure is measured by use of a transducer mounted near
the fuel manifold. This transducer produces an electrical signal
which is translated for the cockpit-mounted indicator in gallons-per­
hour.
Oct 4/01
7-25