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MOTIVE FLOW
FUEL FEED
SOV
PRIMARY
PUMP
FUEL/ OIL
HEAT
EXCHANGER
OIL IN
CENTRIFUGAL
PUMP
FUEL PUMP UNIT
SECONDARY
PUMP
DCUs
EICAS
SL
AVE
MAST
E
R
N1
AMPLIFIER
(ECU)
P
COLLECTOR
TANK
BOOST
PUMP
FILTER
MAIN
EJECTOR VG ACTUATORS
N2
OVERSPEED
GOVERNOR
N1
METERING
VALVE
VG
SCHEDULE
FUEL FLOW
TRANSMITTER
N2
GOVERNOR
TRUST
LEVERS
REV 56, Jan 31/03
Vol. 1 20--50--4
POWER PLANT
Fuel System
Flight Crew Operating Manual MASTER
CSP A--013
A. Engine Overspeed
An N2 overspeed governor in the MFC trims the fuel flow if the N2 speed exceeds
103%.
N1 speed is normally limited by the N1 amplifier. A red overspeed tick mark is on the
analog scale at 98.6%. If the N1 exceeds 98.6%, the digital readout and pointer turn
red and flash for 4 seconds.
2. Automatic Performance Reserve
The automatic performance reserve (APR) system (which is part of the DCU logic) provides
automatic engine failure detection and subsequent thrust increase on the good engine
during takeoff and climb. The APR feature is armed when:
S The APR ARM switch, on the ENGINE CONTROL panel, is set to ARM
S Both ENG SPEED switches (on the ENGINE CONTROL panel) are set to ON
S Aircraft has weight--on--wheels (WOW)
S Both engines N1 is greater than 79%
S Two DCU’s must be serviceable.
When all the above conditions are met, a green APR ARM advisory message is posted on
the EICAS status page.
During takeoff or climb, if the N1 on either engine decreases below 67.6% for any reason,
the DCU’s will supply a signal to the N1 amplifier which will then signal the FCU to increase
the N1 speed 2.3% on the good engine for 5 minutes. The engine with the N1 drop will
revert to N2 mechanical control and will not follow N1 commands An APR icon will also
appear in the center of the N1 gauge of the good engine and the advisory message APR
ARM will be removed. The EICAS will also reset the ITT scale red line on the good engine
from 900 _C to 928_C.
NOTE
The APR does not affect or override thrust lever inputs
to the FCU. It is possible to advance the thrust levers
and obtain power settings higher than normal takeoff
thrust. With higher than normal takeoff thrust settings,
followed by a thrust loss on one engine, the good
engine will respond to the APRcommands to increase
thrust which may result in the ITT limits being
exceeded.
Vol. 1 20--50--5
REV 56, Jan 31/03
POWER PLANT
Fuel System
Flight Crew Operating Manual
CSP A--013
MASTER
Engine Speed Control <MST>
Figure 20---50---2
Engine Control Panel
Centre Pedestal
Engine Speed L/R
Control Switches
Two--position switches
used to set engine
speed control via
electronic or
mechanical modes:
ON -- Engine speed
control is in N1 mode
when N1 rpm exceeds
79.1 per cent.
OFF -- Engine
speed control is in N2
mode regardless of N1
rpm.
<0019>
APR Selector switches
Used to arm, test
and/or disable APR
system.
ARM -- Arms APR
system if both (L/R)
ENG SPEED switches
are at ON (both engines
in N1 speed control
mode).
OFF -- Disables APR
system (APR will not
trigger if one engine
is throttled back).
TEST 1, 2 -- Tests
APR circuits.
TEST 1, 2, 3 -- Tests
APR circuits.
<0019>
3. N1 THRUST SETTINGS <0039>
The FMS is capable of calculating the N1 thrust limits and displaying them on the EICAS
primary page. The calculations are based on pressure altitude, static air temperature and
indicated airspeed. Calculated N1 thrust limits are provided for:
S Takeoff (TO)
S Go--around (GA)
S Climb (CLB)
S Cruise (CRZ)
S Maximum continuous thrust (MTC)
S Flex thrust (FLX).
The FMS calculated N1 value is selected on the THRUST LIMIT page of the FMS CDU. and
displayed on the primary page as:
S Digital reference
S Thrust mode annunciation
S Caret or doughnut.
REV 56, Jan 31/03
Vol. 1 20--50--6
POWER PLANT
Fuel System
Flight Crew Operating Manual MASTER
CSP A--013
The thrust mode annunciation defines the thrust limit that has been selected while the digital
reference provides the value of the setting. Calculated TO, GA and MCT limits are displayed
as a cyan caret. When CRZ is set, the N1 caret is replaced with a white doughnut to
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