CESSNA
SECTION 7
MODEL 172S NAV III
AIRPLANE AND SYSTEMS DESCRIPTION
FUEL SYSTEM
(Continued)
FUEL INDICATING SYSTEM (Continued)
In addition to low fuel annunciation, the warning logic is designed to
report failures with each transmitter caused by short or open circuit
conditions. If the circuit detects any one of these conditions, the
affected fuel indicator will display a red "X". A red X through the top
part of the indicator indicates a sensor failure in the left tank. A red
X through the bottom part of the indicator indicates a sensor failure
in the right tank.
Fuel flow is measured by use of a turbine type transducer mounted
between the fuel/air control unit and the fuel distribution unit. This
flow meter produces a digital signal that is displayed as the rate of
fuel flow on the FFLOW GPH indicator on the EIS pages. FFLOW
GPH is either a horizontal analog indicator or a digital value,
depending on the active EIS page. For fuel consumption
information, a fuel totalizer function is provided on the SYSTEM EIS
page as GAL USED. This digital indicator shows total fuel used
since last reset of the totalizer. To reset the fuel totalizer, the
SYSTEM EIS page must be active and the softkey RST USED must
be selected. The fuel totalizer provides no indication of the amount
of fuel remaining in each tank, and should only be used in
conjunction with other fuel management procedures to estimate total
fuel remaining.
AUXILIARY FUEL PUMP OPERATION
The auxiliary fuel pump is used primarily for priming the engine
before starting. Priming is accomplished through the fuel injection
system. If the auxiliary FUEL PUMP switch is accidentally placed in
the ON position for prolonged periods (with MASTER switch turned
on and mixture rich) with the engine stopped, the engine may be
flooded.
The auxiliary fuel pump is also used for vapor suppression in hot
weather. Normally, momentary use will be sufficient for vapor
suppression; however, continuous operation is permissible if
required. Turning on the auxiliary fuel pump with a normally
operating engine pump will result in only a very minor enrichment of
the mixture.
(Continued Next Page)
172SPHAUS-00
U.S. 7-39
