
of these jet pumps is to pull fuel through the
transfer lines from the fuselage tank. A main
jet pump (main ejector pump) and a standby
pump are located at the low point in the col-
lector tank to pick up and deliver low-pressure
fuel to the respective engine driven fuel pump.
The engines are fed from the respective wing
tanks, and fuselage fuel automatically flows
forward to the wings before it can be fed to
the engines.
The wing tanks are each connected to the fuse-
lage tank by transfer and vent/expansion lines.
Fuel flows from the fuselage tank into the
wing tanks, requiring no pilot action or con-
trol. Check valves are installed in the trans-
fer lines to prevent fuel migration from
wing-to-wing in sideslip maneuvers and from
wing-to-fuselage in nose-up attitudes.
The two wing tanks are joined to each other
by a crossflow line that connects the output
side of the two standby pumps. A motor driven
crossflow valve separates the two tanks when
closed. Fuel can be transferred from one wing
to the other by opening the crossflow valve
(XFLOW switch) and activating either the left
or right standby pump (L or R STBY switch)
on the fuel control panel (Figure 5-1). The
fuel feed systems to the two engines are en-
tirely separate in normal operation, unless the
crossflow valve is selected open.
The fuel quantity indicating system utilizes ca-
pacitance-type probes to measure fuel quan-
tity in each of the tanks. The probes input to
a dual-channel microprocessor which reads
the voltages of each probe and outputs quan-
tity to the EICAS/MFD displays through the
data acquisition units and EFIS symbol gen-
erators.
WING TANKS
Each wing tank, a wet-wing with no bladder,
extends from the wing root to a point just
short of the winglets. Areas which are not part
of the wing fuel cell are the main landing gear
wheel well, the leading edge forward of spar
1 (wing leading edge heat area), and the trail-
ing edge, aft of spar 3 in the flap, spoiler, and
aileron areas.
The usable fuel capacity of both wing tanks is
approximately 500 gallons (1,892 liters), or
approximately 3,354 pounds (1,521 kg.). The
usable fuel is placarded as 1678 pounds in the
left wing and 1676 pounds in the right wing.
The 2.5 degree wing dihedral makes the in-
board portions of the wing tanks the lowest
areas. The inboard-most section of the wing
tank in this low area is known as the collec-
tor tank. The main jet pumps and electric
standby pumps, which supply fuel to the en-
gines, are located in the collector tanks and re-
main submerged in fuel until the tanks are
nearly empty (Figure 5-1). The collector tank
incorporates flapper-type check valves which
permit flow into the enclosure, but restricts
out-flow.
Four scavenge ejector pumps continuously
supply fuel to the collector tank from other
bays within the wing tank to maintain a full
collector tank (about 20 gallons). Openings at
the top of the enclosure permit excess fuel to
flow back into the outboard wing tank bays.
Each wing collector tank contains a float switch
(Figure 5-1), located at the highest point in the
tank, that trips when the fuel level in the col-
lector tank drops to less than 80% full (ap-
proximately 110#). Low fuel in the collector tank
could be due to low fuel quantity remaining or
a failure of the scavenge jet pumps to concen-
trate fuel in the collector tank. When the float
switch trips due to low fuel in the collector
tank, the CAS will present the advisory message,
“L or R FUEL BAY LOW.”
L E A R J E T 4 5
P I L O T T R A I N I N G M A N U A L
5-2
FOR TRAINING PURPOSES ONLY
FlightSafety
international