BOMBARDIER Challenger 601-3A CL-600-2B16 Pilot Training Manual page 194

Fuel Filter
A bypass fuel filter removes solids from the
fuel. A red pop-out bypass indicator is pro-
vided, as well as a differential pressure switch.
The switch will illuminate an amber FILTER
light (Annunciator Panel Section) on the fuel
control panel and the appropriate master cau-
tion system whenever the pressure differential
across the filter exceeds a preset value. It is
from the fuel filter that fuel temperature is
sensed and displayed on the temperature in-
dicator on the fuel control panel.
Fuel Control Unit (FCU)
The fuel control unit is an engine-driven hy-
dromechanical-electronic unit that has a me-
tering section and a computing section. The
metering section includes a mechanical gov-
ernor, a fuel metering valve, a bypass valve,
a pressurizing valve, a thrust lever-operated
shutoff valve, and an electronic control unit
(ECU) for fan rpm control.
The computing section of the FCU contains re-
lief valves and servos to sense engine param-
eters such as rpm (N
2
pressure (P ), compressor inlet temperature
3
(T C), and the position of the variable-ge-
2
ometry system. An amplifier (ECU) operates
a torque motor to control fan rpm (N
The primary function of the FCU is to control
core engine rpm (N
2
lever position. In addition, the FCU modu-
lates fuel flow to control fan rpm (N
the amplifier (ECU) and the torque motor on
the FCU. (See also "Engine Speed Control
and APR Systems" in this chapter.) Engine
acceleration and deceleration are controlled by
the FCU, based on internal core pressure (P
and inlet temperature (T
The FCU also controls the variable-geometry
system as a function of core engine N
compressor inlet temperature (T
The FCU has a fail-safe schedule in the event
of loss of T C input. In this case, the variable-
2
geometry and the acceleration schedules will
), compressor discharge
).
1
) as a function of thrust
) through
1
C).
2
rpm and
2
C).
2
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CL-600-2B16 PILOT TRAINING MANUAL
revert to a fixed temperature reference. If high
thrust is set at the time of failure, a minor de-
crease in thrust may result. If failure occurs
at idle thrust, possible compressor damage
can result if an attempt is made to accelerate
the engine.
Core engine overspeed in limited three ways:
(1) the N governor in the FCU, (2) the com-
2
puter section (therefore, if the FCU governor
fails, N will be limited to less than maxi-
2
mum allowable transient rpm if the comput-
ing section is operational), and (3) if the
computer or the metering valve servo fails, a
bypass valve will open and reduce fuel flow
to the combustor.
The fan rpm control section of the FCU lim-
its fan rpm as a function of thrust lever posi-
tion (PLA) at power settings representing
takeoff, climb, and cruise. In order to minimize
the thrust lever adjustment during climb, the
fan rpm schedule is biased as a function of fan
inlet temperature (T
thrust producer and fan rpm is used to set
thrust. Fan rpm of both engines should be
matched when the thrust levers are aligned.
Fuel Flow Transmitter
A fuel flow transmitter is located in the me-
tered fuel line from the FCU to provide a cock-
pit indication of fuel flow.
Oil Cooler Bypass
The fuel flow path incorporates a fuel bypass
which routes fuel around the oil cooler during
all engine starts. Until fuel flow reaches 400
pounds per hour (pph), fuel is forced through
the bypass valve only. As fuel flow increases
),
above this level, it is divided between the by-
3
pass valve and the oil cooler until the flow
reaches 500 pph, when all the fuel is routed
through the oil cooler.
). The fan is the primary
2
CL 601-3A 7-9
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