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percent speed, the starter disengages. For ground starts, ignition is deactivated at 50 percent. In
flight, ignition is deactivated at 98 percent.
APU Door Positioning
The APU door is positioned automatically as a function of WeightOnWheels
(WOW), Mach
number and APU speed. When RUN is selected on the APU control panel and the airplane is on
ground, the APU door is commanded to the full open position. When the airplane is in flight, the
FADEC schedules the door position.
AUXILIARY POWER UNIT
REV 41, Jul 08, 2004 Flight Crew Operating Manual
CSP 700−6
Volume 2
05−10−11
APU SYSTEM OPERATING SEQUENCE (CONT'D)
APU Loading
The FADEC controls the ready to load signals, one for electrical loading and one for pneumatic
loading. Electrical loading is activated 2 seconds after the APU speed reaches 99 percent. If the
APU drops below 95 percent, electrical loading is not available (on ground and in flight).
On ground, pneumatic loading is available 60 seconds after the APU reaches 99 percent.
In flight, pneumatic loading is available 2 seconds after the APU reaches 99 percent.
The APU LCV is opened upon receiving a bleed air request from the airplane bleed management
control system or the APU BLEED switch on the BLEED/AIR COND/ANTIICE
panel is selected.
Open and closed positions of the control valve are determined by the status of weightonwheels,
main engine starting and environmental control system signals. The bleed and load management
systems are responsible to ensure that the bleed air request is activated only when another source
of bleed air is not commanded. Example: L engine bleed valve open and/or the R engine bleed
valve open and crossbleed valve opened (control valve remains closed).
The normal position for the APU BLEED switch is AUTO position. The AUTO position
automatically integrates control of the APU LCV and the engine bleed has priority. The manual ON
or OFF position will command the LCV to open or close as selected.
APU Shut down
When the “OFF” position on the APU control panel is selected, the FADEC controls the shut down
sequence. The readytoload
signals are cancelled, commanding the APU load valve closed and
reducing the APU speed to 70 percent (below 20,000 feet) or 100 percent (above 20,000 feet) for
a 60 second cooldown period.
NOTE
If the APU switch is selected to RUN prior to completion of the
60 second cooldown period, the APU returns to 100 percent and
continues normal operation.
After cooldown is completed, the APU FADEC shuts down the APU and all loads and fuel
demands are cancelled. When the speed drops below 25 percent, the inlet door is closed, APU
operating hours and fault information are stored in the FADEC and the APU indications are
removed from EICAS.
If the BATT MASTER switch is selected OFF, fire handle is pulled, or either APU shutoff
switches
(External Services Panel or APU compartment) is selected, the APU FADEC will cancel the
cooldown period and initiate an immediate shut down.
AUXILIARY POWER UNIT
Flight Crew Operating Manual REV 41, Jul 08, 2004
CSP 700−6
Volume 2
05−10−12
APU DOOR OPERATION AND INDICATION
The APU door operation and EICAS indication displays are as follows:
Door Operation
The APU inlet door is located on the upper right fuselage area. It is electrically actuated and is
scheduled opened by the FADEC when the APU control switch is selected to RUN. The door will
be commanded to 100% open for start and onspeed
condition for ground operation. In flight prior
to start, the inlet door will be positioned to either 10 degrees open at 0.85 MACH or 20 degrees
open at 0.40 MACH. The door remains in either position until the APU reaches 20% speed and
then will begin to gradually open until the door has reached the full open position and remains
there.
The inlet door will be commanded to the closed position by the FADEC when the speed drops
below 25% on shut down.
Door Indication
The APU door position is displayed on the EICAS STAT page. It is only indicated when there is a
door fault and appears in conjunction with the “ APU DOOR FAIL” caution message. The
numerical readout is amber when a door fault exists as sensed by the FADEC.
GF0510_008
APU RPM
Indication
Indicates that RUN
position is selected on
the APU control panel.
APU DOOR
Indication
APU EGT
Indication
Indicates that RUN
position is selected on
the APU control panel.
Indicates that a door
failed open condition
exists.
APU DOOR
CKPT (°C) FWD
CABIN (°C)
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