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The variable geometry (VG) system regulates airflow across the N2 compressor by changing the position of the inlet guide
vanes and the stator vane for the inlet and first stage of the compressor. The VG system optimizes the angle of attack of the
airflow at the compressor blades and provides compressor stall and surge protection.
The VG inlet guide vanes and stators are programmed by FADEC and positioned by actuators and mechanical linkage.
High-pressure fuel from the engine fuel metering unit is used to hydraulically move the actuators.
N2 speed is displayed on the EICAS. There is no EICAS indication for the variable geometry system.
ACCESSORY GEARBOX
The N2 compressor drives the engine accessory gearbox. Mounted on the gearbox are:
- Engine lubrication pumps
- Hydraulic pump (EDP 1 or EDP 2)
- Engine fuel pump and fuel metering unit (FMU)
- Air turbine starter
- Integral oil reservoir
- Generator
- Permanent Magnet Alternator (PMA)
The PMA provides three-phase power to each engine control unit (ECU). The ECU measures N2 from one of the three
phase inputs. The PMA is designed to provide the electric power required by the control system and engine at and above
45% N2. This speed is less than the minimum N2 idle speed. The PMA is considered to be the primary source of ECU power,
with 28 VDC from the aircraft being the backup source. Aircraft 28 VDC power is required for starting and shutdown.
POWERPLANT
Volume 2 Flight Crew Operating Manual May 06/2005
18-01-04 CSP 100-6 REV 2
ENGINE FUEL SYSTEM
DESCRIPTION
Fuel is delivered to the fuel injectors at the pressures and flow rates necessary to maintain the desired engine thrust. The
engine fuel system also performs the following functions:
- Compressor variable geometry actuator.
- Cool the engine oil (heat transfer).
- Actuate and lubricate fuel system components.
- Provide motive flow for the scavenge and main ejector pumps.
Combustion fuel can be interrupted by moving the L (R) ENGINE run switches to STOP or by selecting the L (R) ENGINE
FIRE switches. The STOP position shuts off the fuel at the fuel metering unit. The L (R) ENGINE FIRE switch closes the
fuel shutoff valve and the fuel metering valve shutoff valve.
COMPONENTS AND OPERATION
FUEL PUMP
The fuel pump mounted on the accessory gearbox is comprised of three separate pumps contained within a single housing.
The fuel pump provides fuel under high pressure and at flow rate that exceeds the requirements of the engine at any power
setting. Excess fuel is bypassed back through the fuel filter system for re-circulation.
Fuel pump pressure is also 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 warms engine fuel and cools engine oil. The engine fuel temperature is indicated on the FUEL
synoptic page.
A 10 micron fuel filter is used to remove solid contaminants from the fuel. The filter is depicted on the FUEL synoptic
page. An impending fuel filter bypass condition on either engine is reported by an advisory CAS message L(R) ENGINE
FUEL BYPASS. A dual impending fuel filter bypass condition on both engines is reported by a caution CAS
message (ENGINES FUEL BYPASS).
FUEL METERING UNIT
The fuel metering unit (FMU) is an electrohydraulic device that meters and distributes the fuel needed for combustion
based upon control signals from the FADEC system. The FMU’s primary components are the fuel metering valve and pressurizing
and shutoff valve. The metering valve supplies fuel in response to commands from the FADEC to maintain combustion
under all operating conditions. The pressurizing and shutoff valve controls the supply of fuel for combustion.
The FMU also supplies the high-pressure fuel to actuate the VG inlet guide vanes and compressor stator vanes.
FUEL SYSTEM OPERATION
The main fuel ejectors or DC powered boost pumps deliver fuel from the collector tanks via fuel feed manifolds to the engines.
Engine fuel shutoff valves (SOVs) are installed in the manifold to interrupt the supply of fuel to the engines during
a fire. The L (R) ENGINE FIRE switches control the SOVs.
At the engine, the fuel is pressurized, heated, filtered, metered, and distributed to the combustion chamber. All fuel scheduling
is controlled by the FADEC.
POWERPLANT
May 06/2005 Flight Crew Operating Manual Volume 2
REV 2 CSP 100-6 18-01-05
ENGINE CONTROL SYSTEM
DESCRIPTION
The Honeywell AS907 powerplant is controlled by the full authority digital electronic control (FADEC) system.
The FADEC provides a full range of engine control, including thrust reverser control under all steady state and transient
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