g round (Figure 5-1). There are two separate
wing fuel systems, one for each engine, con-
nected by a valve-controlled crossfeed sys-
tem. Each fuel system consists of a nacelle
tank and four interconnected wing tanks,
electrical boost and transfer pumps and an
electrically operated crossfeed valve. Total
usable fuel capacity is 384 gallons.
Three modes of operation are available, each
of which is described briefly.
1. N o r m a l o p e r a t i o n — E a c h e n g i n e
receives fuel from its cor responding
fuel cells and boost pump. The boost
pump is required to provide fuel under
pressure to the engine driven high pres-
sure pump.
2. Automatic crossfeed operation—In the
eve n t o f a b o o s t p u m p f a i l u r e , b o o s t
pressure is obtained by supplying fuel
to both engines, through the crossfeed
valve, from one boost pump. A drop in
output pressure from the failed pump is
sensed by a pressure switch, which au-
tomatically opens the crossfeed valve
when the pressure drops below about 10
psi, and illuminates the low fuel pres-
sure annunciator. The fuel pressure an-
n u n c i a t o r w i l l t h e n e x t i n g u i s h a s
pressure is restored by the boost pump
on the opposite engine.
3. Suction feed—This mode of operation
may be employed after a boost pump
has failed, and allows the use of fuel
from tanks on the side with the failed
p u m p . S u c t i o n f e e d o p e r a t i o n i s o b -
tained by moving the crossfeed valve
control switch from the AUTO position
to the CLOSED position. Vacuum cre-
ated by the engine-driven fuel pump
draws fuel from the nacelle fuel tank.
Suction feed is limited to ten hours cu-
mulative between engine-driven fuel
pump overhauls.
FUEL TANK SYSTEM
The fuel system (Figure 5-2) in each wing
consists of one wing leading-edge bladder-
type tank (40 gallons), two outboard-wing
panel bladder-type tanks (23 gallons and 25
gallons), one center section bladder-type
tank (44 gallons), and the nacelle tank (61
gallons). The total usable fuel capacity of
each wing fuel system is 192 gallons. The
outboard wing tanks supply the center sec-
tion and nacelle tanks by gravity flow. Since
the center section tank is lower than the other
wing tanks and the nacelle tank, the fuel is
transfer red to the nacelle tank by the fuel
transfer pump in the low point of the center
section tank. Fuel for each engine is pumped
directly from its nacelle fuel tank by an elec-
tric boost pump. Each system has two f iller
cap openings; one in the top of the nacelle
tank and one mid-wing in the leading edge
tank. An anti-siphon valve is installed at
each f iller por t to prevent the loss of fuel or
collapse of fuel-tank bladder in the event
the f iller cap is improperly secured.
There is a check valve between the nacelle
tank and the wing tank. Fuel can flow only
into the nacelle tank, not back into the wing
tank. If a full fuel load is needed, f ill the na-
celle tank f irst, then f ill the wing tank.
The heated fuel vent and the NASA integ ral
ram scoop vent work together to prevent the
bladders from collapsing as fuel is drawn
out of them.
Each nacelle tank is connected to the engine
on the opposite side by a crossfeed line for
single-engine or failed boost pump opera-
tion. Crossfeed operation is automatic de-
pending on the boost pump selected in the
feeding nacelle tank. This system makes it
possible for fuel in either wing system to be
available to either engine, or both engines
simultaneously.
KING AIR C90GTi/C90GTx
PILOT TRAINING MANUAL
5-2
FOR TRAINING PURPOSES ONLY
5
FUEL
SY
STEM
Summary of Contents for C90GTi
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