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engine thrust. The engine fuel system, in addition to providing fuel for combustion, is used for:
• Controlling and actuating the VG compressor linkage;
• Cooling the engine oil (heat exchange);
• Actuating and lubricating servos within the Fuel Control Unit (FCU); and
• Providing motive flow for the main ejector and scavenge ejector pumps.
Combustion fuel can interrupted by moving the thrust lever to SHUTOFF or by selecting the
engine FIRE PUSH switch/light. The SHUTOFF position shuts off the fuel at the FCU. The FIRE
PUSH switch/light closes the fuel shutoff valve.
Components and Operation
Engine-Driven Fuel Pump
The accessory gearbox-mounted fuel pump is comprised of three separate pumps contained
within a single housing. The engine-driven fuel pump provides high-pressure fuel at a flow rate
that exceeds the requirements of the engine at any power setting. Fuel pump pressure is used
to generate motive flow for the scavenge and main ejectors of the aircraft fuel system.
Fuel/Oil Heat Exchanger and Fuel Filter
A fuel/oil heat exchanger is used to warm engine fuel and cool engine oil. The fuel temperature
at the fuel filter is indicated on the EICAS status page. A fuel filter is used to remove solid
contaminants from the fuel. If the filter becomes clogged, the fuel bypasses the filter to ensure
continued operation. A clogged filter is indicated by the L(R) FUEL FILTER caution EICAS
message.
Fuel Control Unit (FCU)
The fuel control unit is a hydromechanical metering device that supplies fuel in response to
mechanical inputs from the thrust levers. In addition, the FCU controls and actuates the VG inlet
guide vanes and stator vanes of the engine compressor.
During start and at low power, the FCU hydromechanically schedules the fuel.
POWER PLANT
Description
Vol. 2 19−10−3
REV 66, Feb 01/07
CL−604 Operating Manual
PSP 604−6
ENGINE FUEL SYSTEM (CONT'D)
Engine Fuel System − Schematic
Figure 19−10−2
POWER PLANT
Description
Vol. 2 19−10−4
REV 66, Feb 01/07
CL−604 Operating Manual
PSP 604−6
ENGINE FUEL SYSTEM (CONT'D)
Electronic Control Unit (ECU)
When at high thrust settings, the engine is controlled by an electronic control unit (ECU) which
works in tandem with the FCU. The ECU is also referred to as the N1 control amplifier. The ECU
(or N1 control amplifier) trims the FCU fuel output to maintain a N1 speed schedule for a given
thrust lever setting.
Fuel System Operation
N2 Speed Control (N1 < 79%)
At low power settings (N1 below 79%), the FCU hydromechanically controls the N2 speed. In
N2 mode, the FCU adjusts N2 speed so that matched movement of the thrust levers produces
nearly matched N2 rpm for the engines. N1 speeds, fuel flows, or ITT indications may differ
between engines.
N1 Speed Control (N1 > 79%)
At takeoff, climb and cruise power settings (N1 above 79%), the N1 control amplifier controls
the engine N1 rpm. The amplifier trims the FCU fuel output to achieve the desired N1 rpm.
With the ENG SPEED switches selected to ON, automatic switchover from N2 to N1 speed
governing occurs at 79% N1. Matched movement of the thrust levers produces nearly matched
N1 rpm and nearly matched thrust between the engines.
NOTE
If an ENGINE SPEED switch is moved from ON to OFF at high
power settings, the engine will revert to N2 speed control. A rapid
increase in engine acceleration will occur, and an overtemperature
limit may be exceeded.
ENGINE CONTROL Panel
Figure 19−10−3
AUTOMATIC PERFORMANCE RESERVE SYSTEM
Description
During takeoff, the APR system monitors the N1 rpm of both engines. If a significant loss of N1 rpm
is sensed on one engine, the APR system automatically increases the thrust of the remaining
engine to the APR thrust rating.
POWER PLANT
Description
Vol. 2 19−10−5
REV 66, Feb 01/07
CL−604 Operating Manual
PSP 604−6
AUTOMATIC PERFORMANCE RESERVE SYSTEM (CONT'D)
APR activation does not override thrust lever input to the FCU nor does it restrict movement of the
thrust lever.
Operation
The APR system is armed during takeoff when the APR switch is selected to ARM and both
engines’ N1 rpm is above 79% (N1 speed mode). This is indicated by the APR ARM advisory
EICAS message. During a normal takeoff, the advisory message is removed five minutes after
APR arming.
During takeoff, the APR system monitors the N1 rpm of both engines through the DCUs. If an N1
rpm drop below 67.6% rpm is sensed at either engine, the system automatically commands both
　
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