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· Gearbox − Provides the sump for the lubrication system and mounting of component and
accessories.
· Exhaust − The flow across the APU and oil cooler is created by utilizing the exhaust discharge
velocity.
· Monitor zones for fire/overheat/smoke events, FIDEEX system health and status.
APU SYSTEM SCHEMATIC
BLEED AIR
APU COMPARTMENT AIRFLOW
OIL
OUT
OIL
IN
AIR/OIL COOLER
TO APU
COMPARTMENT
GEARBOX
TO AIRCRAFT
BLEED AIR
SYSTEM
LOAD CONTROL
VALVE
ELECTRICAL CIRCUITS
THE AIR SYSTEM IS SHOWN WITH AN APU BLEED LOAD
FROM/TO APU
SYSTEMS
FROM/TO
AIRCRAFT
SYSTEMS
FADEC
BLEED AIR
DUCT
BLEED AIR
CHECK VALVE
SURGE VALVE SURGE DUCT
BLEED
DIFFUSER
AIRCRAFT
SKIN
EXHAUST
TURBINE
COMPRESSOR
COMBUSTION
INLET
NOTE
EDUCTOR
INLET AIR
STARTER
GEN
FUEL CONTROL
UNIT
OIL
PUMP
GF0510_003
AUXILIARY POWER UNIT
REV 41, Jul 08, 2004 Flight Crew Operating Manual
CSP 700−6
Volume 2
05−10−3
APU SYSTEM SCHEMATIC (CONT'D)
Lubrication
The lubrication system incorporates an integral oil reservoir. The two main areas that are
lubricated are the gearbox and turbine bearings.
The gearbox sump is the reservoir and can be filled through the fill cap. The APU can also be
serviced on ground only, using the airplane remote oil replenishment system, simplifying post flight
maintenance actions.
The lubrication system consists of the following components:
· Oil filters − Lube and generator scavenge.
· Oil temperature sensor − Sends an input to the FADEC for both minimum oil temperature
and high oil temperature protection. When oil temperature increases to a high
predetermined value for 10 seconds, the APU (on ground only) will shut down.
· Low Oil Pressure (LOP) switch − When pressure drops below a predetermined PSIG after
the APU has reached onspeed
(not less than 99%) for 15 seconds, the APU (on ground
only) will shut down automatically.
· Oil cooler − Will bypass oil at a predetermined lower than normal operating temperature and
flow through the cooler when temperatures are above the normal operating range.
· Magnetic Chip Collector (visual inspection) − Provides visual indication of metal particles
within the system.
Oil Pressure
On the prestart BITE check, the LOP switch is checked by the FADEC. During operation, if oil
pressure decreases below a predetermined PSIG for approximately 15 seconds (on ground),
automatic shut down will occur and an “APU OIL LO PRESS” caution message will come on.
A low oil pressure condition in flight will not cause an APU protective shut down.
Gravity Oil Fill
The APU oil sump can be filled through the gravity fill cap. The oil reservoir for the APU is an
integral part of the accessory gearbox assembly and has a capacity of 5.25 quarts, with the add
level at 3.75 quarts. The gravity fill is designed for a “fill to spill” ease of servicing and used only
when the oil replenishment system does not function.
OIL REPLENISHMENT SYSTEM
The oil replenishment tank volume contains 5.7 liters (6 US quarts). APU oil level is measured via a
sensor located in the APU oil tank which provides quantity information for the EICAS STAT page.
Electrical failure of this sensor will be detected during the builtintest
and the quantity indicating
value will change from a numerical value to amber dashes on EICAS. An “APU OIL LO QTY”
advisory message will occur on EICAS (on ground only), when the APU oil level reaches
approximately 3.5 US quarts and the APU has not been operating for 15 minutes.
AUXILIARY POWER UNIT
Flight Crew Operating Manual REV 41, Jul 08, 2004
CSP 700−6
Volume 2
05−10−4
OIL REPLENISHMENT SYSTEM (CONT'D)
An oil replenishment tank is located in the aft equipment bay and contains an electrical pump and
sensor probe for quantity level. The oil replenishment (pressure filling) system is designed for
ground use only and serves both main engines and APU. A three way electrical valve is incorporated
in the replenishment system to allow transfer of oil to the system being topped up (either engine or
APU).
APU/ENGINE OIL
REPLENISHMENT TANK
APU OIL TANK
APU OIL QUANTITY
Indicates APU oil tank
quantity in quarts.
NOTE
are removed when the airplane is not on
ground or APU is operating greater than
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