Cessna 402C - Page 227

G~·402C
MODEL
FUEL FLOW GAGE
SECTION 7
AIRPLANE & SYSTEMS DESCRIPTIONS
The fuel flow gage, see Figure 7-1, is a dual instrument which indicates
the fuel consumption of each engine in pounds per hour. The fuel flow gage.
used with the injection system senses the pressure at which fuel ;s deliv-
ered to the engine spray nozzles. Since fuel pressure at this point is
proportional to the fuel consumption of the engine, the gage ;s marked as a.
flowmeter.
The gage dial is marked with arc segments corresponding to proper fuel
flow for various power settings and maximum power altitudes and is used as
a guide to quickly set the mixtures. These gage markings are predicated on
the use of 100 grade aviation fuel. Increase fuel flow 2% above markings
when 100LL grade aviation fuel is used.
The gage has takeoff, climb and cruise markings for various percentages
of power. The takeoff range (white arc) presents the desired fuel flow
(full rich schedule for proper engine cool ing) for full power (2700 RPM and
39.0 inches Hg. manifold pressure) operation under all conditions up to
12.000 feet altitude. The climb range (blue segments) presents the desired
fuel flow for best power mixture at 75% power with an enriched mixture for
higher power settings to allow proper engine cool ing during cl imb condi-
tions. The cruise range presents the desired fuel flow for recommended
lean mixture at the specified percent power.
FUEL QUANTITY GAGE
The dual indicating fuel quantity gage. see Figure 7-1, is calibrated in
pounds and will accurately indicate the weight of fuel contained in the
tanks regardless of whether 100 grade aviation or 100LL grade aviation fuel
is used; however, fuel density varies with temperature, therefore a full
tank will weigh more on a cold day than on a wal11l day. This will be re-
flected by the weight shown on the gage. A gallons scale is provided in
blue on the indicator for convenience in allowing the pilot to detel11line
the approximate volume of fuel on board. The volume markings are predi-
cated on the use of 100 aviation grade fuel. Reduce the indicated gal-
~~ lonage reading by 4% when lOOLL grade aviation fuel is being use~.
FUEL LOW LEVEL WARNING LIGHTS
The optional fuel low level warning lights. see Figure 7-3, provide a
warning
when the left and/or right main tanks contain approximately 60
pounds of fuel. Thewarnin9 is provided by the L FUEL LOW and R FUEL LOW
lights located on the annunciator panel. These lights are actuated by a
~ float switch located in- each main fuel tank. Each light operates inde-
pendently from the fuel quantity indicating system.
ENGINE-DRIVEN FUEL PUMPS
Each engi ne is equi pped wi th a mechanically driven fuel pump which
provides fuel to the metering unit. Each pump also contains a bypass which
returns excess fuel and vapor to the main tanks at all times. Should these
, .. ~ pumps fail, the main tank auxiliary pumps can provide sufficient fuel flow
for all partial-power engine operations. These auxiliary pumps. however.
operate at a fixed pressure, consequently the mixture must be leaned when
operating at a low power setting to prevent flooding of the. engi~e. Con-I
versely, if an engine-driven pump fa ilure should occur dunng hlgh power
operation. adequate fuel flow may not be available to ensure rated powerl
and adequate
engine cooling.
1 November 1979
Revision 4 - 1 December 1983
7-23