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provides a signal to generate a “L/R FUEL
FILTER” CAS message (Table 7-4) to indicate
an impending fuel filter bypass situation when-
ever a 6-8 PSID differential is detected. If the
differential pressure exceeds 9-12 PSID, fuel
will bypass the filter and flow unfiltered to the
inlet of the high pressure element of the en-
gine-driven pump.
An amber “L or R FUEL FILTER” CAS mes-
sage will appear if the respective engine or air-
frame fuel filter has an impending bypass
while on the ground. While in flight, the CAS
message will be white.
FUEL CONTROL UNIT (FCU)
The fuel control unit (FCU) is mounted on
the aft side of the engine-driven fuel pump
(Figures 7-15 and 7-16). The primary function
of the FCU is to schedule fuel flow to the fuel
manifold. The normal mode of operation is
computer-on. In the computer-on mode, the
torque motor (Figure 7-16) in the FCU re-
sponds to electrical signals from the fuel com-
puter (DEEC). The backup mode of operation
is manual mode. In manual, the metering valve
(Figure 7-16) in the FCU responds hydrome-
chanically to thrust lever movement.
The FCU includes (Figure 7-16):
• A DC torque motor which schedules fuel
in the computer-on mode in response to
the DEEC. When in manual mode, the
torque motor valve goes full open.
• A metering valve which (1) meters fuel
flow in the manual mode in response to
thrust lever movement and (2) limits
fuel flow in the computer-on mode in re-
sponse to the 105% flyweight governor.
The metering valve is normally full open
during computer-on operation.
• An ultimate overspeed solenoid valve
which is normally open, but is energized
closed by the DEEC at 107% N1 or 109%
N2 to shut off fuel. Operates with com-
puter-on or with MAN selected.
• A manual shutoff valve, operated me-
chanically by thrust lever movement be-
tween CUTOFF and IDLE. Operates
with computer-on or in manual.
• A manual mode solenoid which is nor-
mally energized open by the DEEC dur-
ing computer-on operation.
• Pneumatic circuits to channel and con-
trol P3 bleed-air pressure to pneumat-
ically position the metering valve.
• A mechanical flyweight governor, driven
by N2 to (1) limit engine overspeed to
105% in the computer-on and computer-
off modes and (2) govern engine rpm
relative to thrust lever position in the
manual mode.
FUEL FLOW SENSOR
Each engine has a fuel flowmeter (sensor) lo-
cated between the FCU and the engine fuel
manifolds (Figure 7-16). The flowmeter com-
pensates for fuel temperature changes to de-
termine fuel flow mass and provides this
information to the dual fuel flow converter
(DFFC) located within the tailcone. The dual
channel DFFC sends the fuel flow information
to the DAUs which convert the information to
ARINC 429 bus format, then passes it on to the
symbol generators in the IC-600 integrated
computers. The symbol generator then pro-
vides fuel flow information for display in the
engine instrument section of the EICAS
(Figure 7-5).
Fuel flow information is also sent from the
DAUs to the FMS(s) for fuel burned and fuel
remaining computations and displays.
The DFFC has built-in redundancies should
one output channel fail. The converter oper-
ates on DC power through two circuit break-
ers, labeled L/R FUEL FLOW, located in the
engine group on the left and right circuit
breaker panels respectively.
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
7-22
FOR TRAINING PURPOSES ONLY
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