APS 2000 Auxiliary Power Unit
Training Course
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Section 2410 of the export administration act. Include this notice with any reproduced portion of this document.
This document is intended as a training aid only. Refer to the applicable manufacturer’s technical manual for specific procedures. Sundstrand Aerospace reserves
the right to make changes in specifications and other information contained in this publication without any prior notice. The user should in all cases consult
Sundstrand Aerospace to determine whether any such changes have been made.
NLR-NO LICENSE REQUIRED
SPS CT/MAY 1999
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SUNDSTRAND AEROSPACE
APS 2000 Auxiliary Power Unit
Front Matter
SPS CT/MAY 1999
Page i
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SUNDSTRAND AEROSPACE
TABLE OF CONTENTS
SUBJECT
PAGE
SUBJECT
SECTION
Preface............................................................................................ iii
Introduction...................................................................................... 1
Abbreviations and Acronyms ...........................................................v
Installation ....................................................................................... 2
APU Leading Particulars................................................................ vii
APU Theory..................................................................................... 3
Engine Assembly............................................................................. 4
Gearbox Assembly .......................................................................... 5
Lubrication System.......................................................................... 6
Pneumatic System .......................................................................... 7
Fuel System .................................................................................... 8
Electrical System............................................................................. 9
Start/Stop Sequence ..................................................................... 10
Line Replaceable Units ................................................................. 11
Maintenance Inspections .............................................................. 12
Fault Isolation ................................................................................ 13
Troubleshooting ............................................................................ 14
SPS CT/MAY 1999
Page ii
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SUNDSTRAND AEROSPACE
PREFACE
FAA AND AIRCRAFT MANUFACTURER APPROVED
PUBLICATIONS
GENERAL DESCRIPTION
The APS 2000 Auxiliary Power Unit Training Course, developed by
the Customer Service Training Group of Sundstrand Aerospace, is
designed to give the student an understanding of the various
components of the Auxiliary Power Unit (APU) and their functions.
This course also provides routine maintenance and troubleshooting.
The airline is provided a variety of FAA and aircraft manufacturer
approved publications for the APS 2000 APU. These publications
include:
Aircraft Flight Crew Manuals
STUDENT WORKBOOK
Aircraft Maintenance Manuals
This workbook is intended for the “limited” purpose of providing
component familiarization, general data, and support information for
this training course.
Engine and Component Maintenance Manuals
Service Bulletins
This is an uncontrolled document and will not be updated or revised
on a regular basis. Specific values given in this document such as
speed, temperature, and pressure are provided for the purpose of
illustration and are not necessarily representative of the true values
of the APS 2000 APU.
Chapter 49 of the aircraft maintenance manual presents detailed
APU and LRU removal and installation procedures plus maintenance
and servicing techniques that can be accomplished at the flight line.
Careful study of chapter 40 will add to the student’s expertise in
troubleshooting and maintaining the Sundstrand APS 2000 APU.
SPS CT/MAY 1999
Page iii
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SUNDSTRAND AEROSPACE
AIRCRAFT APPLICATIONS The information presented in this course applies to the following
aircraft:
BOEING 737
SPS CT/MAY 1999
Page iv
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SUNDSTRAND AEROSPACE
ABBREVIATIONS AND ACRONYMS
The following list contains the abbreviations and acronyms that are used throughout this training manual.
A/D
AC
ACMS
APIC
APS
APU
APUCU
ARINC
ATA
AVAIL
BATT
BCV
BITE
CB
CMM
CPU
D/A
DC
ECU
ECS
EGT
EMU
ETOPS
FADEC
FAR
PMG
Analog/Digital
Alternating Current
Aircraft Condition Monitoring System
Auxiliary Power International Corp.
Auxiliary Power System
Auxiliary Power Unit
Auxiliary Power Unit Control Unit
Aeronautical Radio Corp.
Air Transport Association
APU Available
Battery
Bleed Control Valve
Built-in Test Equipment
Circuit Breaker
Component Maintenance Manual
Central Processing Unit
Digital/Analog
Direct Current
Electronic Control Unit
Environmental Control System
Exhaust Gas Temperature
Event Monitoring Unit
Extended Twin Engine Operations
Full Authority Digital Electronic Controller
Federal Airworthiness Regulation
Permanent Magnet Generator
FCU
FOD
FWD
GBX
GCU
GMT
HOT
ID
IPC
ISA
LOP
LP
LRU
MAX
MES
MIN
MMEL
MTBF
MTBUR
N
NVM
OAP
OAT
Pcd
P/N
PS
SPS CT/MAY 1999
Fuel Control Unit
Foreign Object Damage
Forward
Gearbox
Generator Control Unit
Greenwich Mean Time
High Oil Temperature
Identification
Illustrated Parts Catalog
International Standard Atmosphere
Low Oil Pressure
Low Pressure
Line Replacement Unit
Maximum
Main Engine Start
Minimum
Master Minimum Equipment List
Mean Time Between Failure
Mean Time Between Unscheduled Removals
Rotation Speed
Non Volatile Memory
Outside Air Pressure
Outside Air Temperature
Pressure Compressor Discharge
Part Number
Power Section
Page v
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SUNDSTRAND AEROSPACE
ABBREVIATIONS AND ACRONYMS (Continued)
PWA
RAM
ROM
RTD
RTL
SHP
S/N
SPS
TRU
TSO
US G
Printed Wiring Assembly
Random Access Memory
Read Only Memory
Resistive Temperature Device
Ready To Load
Shaft Horsepower
Serial Number
Sundstrand Power System
Transformer Rectifier Unit
Technical Standard Order
US Gallon
°C
Degrees Celsius
°F
>
<
Degrees Fahrenheit
Is Greater Than
Is Less Than
±
Plus or Minus
Ω
Ohm
∆
Differential
°
%
cc/h
dB
Degree
Percent
Cubic Centimeter per Hour
Decibel
ft
HP
Hz
kg
kHz
kPa
kW
lb.
lbs/hr
lbs/min
m
mA
MHz
mm
mV
PSIA
PSID
PSIG
RPM
VAC
VDC
SPS CT/MAY 1999
Feet
Horse Power
Hertz
Kilogram
Kilo Hertz
Kilo Pascal
Kilo Watt
Pound
Pounds per Hour
Pounds per Minute
Meter
Milliampere
Mega Hertz
Millimeter
Millivolt
Pounds per Square Inch Absolute
Pounds per Square Inch Differential
Pounds per Square Inch Gauge
Revolutions per Minute
Volts, Alternating Current
Volts, Direct Current
Page vi
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SUNDSTRAND AEROSPACE
LEADING PARTICULARS
WEIGHT
296 lbs (dry)
OPERATING ALTITUDE
-1000 to 37,000 ft
SEA LEVEL 59° STD DAY – UNINSTALLED PERFORMANCE
OUTPUT SHAFT HORSEPOWER
95 HP
ROTOR SPEED
100% (45,225 RPM)
ROTOR OVERSPEED (SHUTDOWN)
105% (47,486 RPM)
ROTOR UNDERSPEED (SHUTDOWN)
97% (43,868 RPM)
BLEED AIRFLOW
171 LBS/MIN
BLEED AIR PRESSURE
42 PSIG
SPS CT/MAY 1999
Page vii
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SUNDSTRAND AEROSPACE
LEADING PARTICULARS (Continued)
EXHAUST GAS TEMPERATURE LIMITS
During the start sequence, one of the three maximum EGT limits will be used by the Full Authority Digital Electronic Controller (FADEC) depending
on altitude and/or ambient temperature at start. The ambient temperature signal is provided by the Event Monitoring Unit (EMU) and the altitude
signal is provided by the pressure transducer. Both signals are sent to the FADEC.
Condition 1:
Altitude above 25,000 feet or ambient temperature below -17.8°C
Condition 2:
Altitude between 15,000 feet and 25,000 feet and ambient temperature above -17.8°C
Condition 3:
Altitude below 15,000 feet and ambient temperature above -17.8°C
% Speed
Condition 1
Condition 2
Condition 3
0
1100
760
760/843
30
1100
760
760/843
55
1100
760
760/843
60
1100
760
760/843
98
899
760
760/843
98 + .5 sec
899
760
760/843
FADEC overtemperature timers for the three above conditions:
Condition 1 = 10 seconds
Condition 2 = 4 seconds
Condition 3 = 760°C for 10 seconds or 843°C for 1 second
SPS CT/MAY 1999
Page viii
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SUNDSTRAND AEROSPACE
LEADING PARTICULARS (Continued)
GEARBOX SPEEDS:
OIL PRESSURE
Input
45,225 RPM
Starter
32,444 RPM (output)
Fuel Control
10,200 RPM (output)
Oil Pump
10,200 RPM (output)
Cooling Fan
30,458 RPM (output)
Generator
6,000 RPM (output)
20 PSIG (minimum)
45 PSIG (normal)
OIL CAPACITY
3.3 Qts (full)
2.0 Qts (add)
OIL TEMPERATURE (SHUTDOWN)
275°F
APPROVED OILS SPECIFICATION
MIL-L-7808
MIL-L-23699
CAUTION:
DO NOT MIX OR SUBSTITUTE OIL SPECIFICATIONS. USE ONLY
ONE OF THE APPROVED OILS. IF THE OIL SUPPLY IS LOW AND
THE OIL BEING USED IS NOT AVAILABLE, DRAIN THE OIL SUMP
AND CHANGE THE OIL FILTER. SERVICE THE OIL SYSTEM WITH
AN APPROVED OIL.
SPS CT/MAY 1999
Page ix
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SUNDSTRAND AEROSPACE
LEADING PARTICULARS (Continued)
APPROVED FUELS
Fuel Type
Specification
Temperature Range
Jet A
ATSM D1655 (NATO Code F-35)
-30°F (-35°C) to +135°F (+57°C)
Jet A-1
ATSM D1655 (NATO Code F-35)
-45°F (-43°C) to +135°F (+57°C)
Jet B
ATSM D1655 (NATO Code F-45)
-65°F (-54°C) to +135°F (+57°C)
JP-4
MIL-T-5624 (NATO Code F-40)
-65°F (-54°C) to +135°F (+57°C)
JP-5
MIL-T-5624 (NATO Code F-44)
-30°F (-35°C) to + 200°F (+93°C)
JP-8
MIL-T-83133 (NATO Code F-34)
-30°F (-35°C) to + 200°F (+93°C)
SPS CT/MAY 1999
Page x
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SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 1
INTRODUCTION
SPS CT/MAY 1999
Page 1.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
AUXILIARY POWER UNIT
APU CONTROL SYSTEM
The APS 2000 Auxiliary Power Unit (APU) is a gas turbine powered
system that is designed to provide auxiliary electrical and pneumatic
power to the aircraft on the ground and in flight.
The APU control system consists of a Full Authority Digital Electronic
Controller (FADEC), APU Control Unit (APUCU) and various valves,
motors and sensors. Startup, run and shutdown of the APU is
controlled by the FADEC and the APUCU, during run operation the
rotor is maintained at 100% engine speed during all load conditions.
Ambient air is delivered to the APU through the aircraft duct system,
the air is compressed by the compressor impeller and is used to
operate the APU and to provide bleed air to the aircraft
Environmental Control System or the Main Engine Start system.
Bleed air from the APU is controlled by the APU bleed valve. The
remaining compressed air is heated in the combustor chamber with
fuel provided by the APU fuel system and is used to drive the turbine
wheel. The turbine wheel uses the heated air energy to drive the
compressor impeller and the gearbox. The heated air then exits
through the APU exhaust system.
The APU is constantly monitored by the FADEC while in operation,
should a fault condition occur it will be recorded and stored in the
memory of the FADEC, this information can be viewed in the fault
display window on the front face of the FADEC.
The gearbox mounted generator provides electrical power to the
aircraft systems when required. The gearbox also drives an oil pump
for lubrication, electronic fuel control for fuel metering, and a cooling
fan to provide cooling air to the oil cooler and the generator.
SPS CT/MAY 1999
Page 1.1
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SUNDSTRAND AEROSPACE
Figure 1-2. Auxiliary Power Unit
SPS CT/MAY 1999
Figure 1-1. APU Control System
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Page 1.2
SUNDSTRAND AEROSPACE
FULL AUTHORITY DIGITAL ELECTRONIC CONTROLLER
APU CONTROL UNIT
The electronic control unit is a microprocessor based Full Authority
Digital Electronic Controller (FADEC). The FADEC is connected to
the APU by means of the aircraft electrical system and the APU
engine electrical harness. The FADEC monitors and controls engine
operation.
The APU Control Unit (APUCU) consists of relays, a printed circuit
board and control circuits. The Control Unit circuitry assists in
sequencing electrical control signals for APU and aircraft systems
operation.
SPS CT/MAY 1999
Page 1.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 1-3. Full Authority Digital Electronic Controller
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Figure 1-4. APU Control Unit
Page 1.4
SUNDSTRAND AEROSPACE
COMPONENT LOCATION
The APU is located in the tail section of the aircraft and is mounted
inside a sound reducing fireproof shroud.
The FADEC is located in the aft cargo compartment near the
compartment door.
The APU Control Unit is mounted in the electronics compartment of
the aircraft.
There are two APU control panels provided for operation of the APU.
Located on the flight deck forward overhead panel is the APU start
switch, warning lights, exhaust temperature and AC ampere meter.
The ground control panel is located in the right wheel well, this panel
can be used in the event of a fire on the ground.
SPS CT/MAY 1999
Page 1.5
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 1-5. APU Component Location
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Page 1.6
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 2
INSTALLATION
SPS CT/MAY 1999
Page 2.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
The APU is located in the tail section of the aircraft and is enclosed
in a sound reducing titanium shroud. The shroud is constructed in
two sections; the Upper shroud that is attached to the aircraft
structure by four struts and the Lower shroud that is secured by ten
latches to the Upper shroud. The Lower shroud must be removed
when inspection or repairs to the APU are required.
A hinged Access Door is located at the bottom side of the aircraft tail
section structure and provides access to the APU compartment. The
door is secured in the closed position by three latches.
UPPER SHROUD
The Upper Shroud provides three APU engine mounts, fuel inlet line,
fuel heat system, electrical connections, bleed air duct connections
and the APU air inlet and cooling fan ducts. The air inlet duct lock
handle secures the air inlet duct in its proper position and must be in
the locked position before the Lower Shroud can be installed.
LOWER SHROUD
An oil service access port is located on the left side of the shroud.
Removing the oil service cap allows oil servicing of the APU without
removing the Lower shroud. The accessory cooling air overboard
exhaust, located on the right side of the shroud, allows cooling fan
air to exhaust overboard through the APU compartment access door.
SPS CT/MAY 1999
Page 2.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 2-1. APU Shroud
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Page 2.2
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 3
APU THEORY
SPS CT/MAY 1999
Page 3.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
THEORY OF OPERATION
The combustion process begins when the start fuel system is
activated, the fuel is injected into the combustor chamber and ignited
by the ignition system. The burning fuel expands the gasses in the
combustor chamber and accelerate through the turbine nozzle, the
gasses impinge on the blades of the turbine wheel and cause the
turbine wheel to rotate.
For the turbine engine to operate, it is necessary to have an airflow
supply for the combustion process. The compressor impeller
mounted on the rotor assembly shaft provides the airflow.
The rotating turbine wheel drives the compressor impeller, gearbox
and the gearbox accessories. The gasses flowing from the turbine
wheel then exit into the exhaust system.
The power to turn on the engine Rotor Assembly is initiated by the
starter. The starter rotates the gears in the gearbox, which in turn
drives the rotor assembly.
At a determined engine speed the main fuel system is activated and
the starter, start fuel system, and ignition system are de-activated.
The engine is now self sustaining in operation as long as the main
fuel system is delivering fuel to the combustor.
The APS 2000 is a continuous cycle, centrifugal flow engine, using a
centrifugal flow compressor impeller and turbine wheel mounted on a
common shaft. The engine operates at a constant speed for all
operational requirements.
Air is drawn into the engine by the rotating compressor impeller, the
air then flows to the diffuser where the air slows and the pressure is
increased by the action of the diffuser. The diffuser also aligns the air
flow for delivery to the combustor chamber where the air is mixed
with fuel for combustion.
Not all of the compressed air produced by the APU is used for
combustion, the excess air is available as bleed air to operate the
aircraft pneumatic systems.
SPS CT/MAY 1999
Page 3.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 3-1. APU Theory
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Page 3.2
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 4
ENGINE ASSEMBLY
SPS CT/MAY 1999
Page 4.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
The Engine Assembly is a gas turbine engine that is designed to
provide shaft horsepower to drive an AC generator and provide
bleed air to the aircraft pneumatic systems. The Engine Assembly
consists of two modules and are identified as the Turbine Assembly
and the Combustor Assembly.
TURBINE ASSEMBLY
The Turbine Assembly is comprised of the air intake housing,
diffuser, rotor assembly, and the turbine nozzle and containment
ring.
COMBUSTOR ASSEMBLY
The Combustor Assembly consists of the combustor housing,
combustor chamber, and a start and main fuel manifold assembly.
Air is discharged into the combustor housing from the compressor
impeller where the air is extracted through a bleed air port to the
aircraft pneumatic systems when required. The combustor housing
also forms a plenum that surrounds the combustor chamber, the air
enters the chamber through dilution holes to support the combustion
process and provide cooling of the APU internal parts.
SPS CT/MAY 1999
Page 4.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 4-1. Engine Assembly
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Page 4.2
SUNDSTRAND AEROSPACE
COMPONENTS
TURBINE ASSEMBLY
ROTOR ASSEMBLY
The Turbine Assembly consists of the following components:
The single stage rotor assembly is a balanced unit that consists of a
overhung radial compressor impeller and turbine wheel that are
mounted on a common shaft and supported by two bearings. The
bearings are located inside a bearing capsule that is secured into
and supported by the air intake housing. A stationary seal plate is
located between the compressor impeller and the turbine wheel, the
seal plate functions as a heat shield and also prevents compressor
impeller air from bypassing into the turbine area.
Air Intake Housing
Diffuser
Rotor Assembly
Turbine Nozzle and Containment Ring
TURBINE NOZZLE AND CONTAINMENT RING
AIR INTAKE HOUSING
The Air intake Housing directs the air to the compressor impeller
while providing a rigid support between the gearbox and the
combustor assembly. The housing also provides the attachment and
support for the rotor assembly, diffuser, and the turbine nozzle and
the containment ring. A two piece intake screen is mounted on the
air intake housing to protect the compressor impeller from foreign
object damage.
DIFFUSER
The Diffuser is bolted to the rear face of the air intake housing, the
function of the Diffuser is to slow down the compressor impeller
airflow and direct the air into the combustor assembly.
The turbine nozzle directs and accelerates the combustor hot gasses
to drive the turbine wheel and is secured into the containment ring by
seven bushings. The containment ring supports the turbine nozzle
and is connected to the diffuser and the air intake housing by four Hblock retainer bolts and nuts.
QUILL SHAFT
The quill shaft provides the mechanical means of connecting the
rotor shaft to the gearbox drive train. The shaft is splined at both
ends and is driven by the oil impeller located on the front of the rotor
assembly.
SPS CT/MAY 1999
Page 4.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 4-2. Turbine Assembly
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Page 4.4
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
AIR INLET DUCT
The Air Inlet Duct surrounds the air intake housing to allow ambient
air to be delivered to the compressor impeller. The Duct is designed
to rotate for the installation of the APU and alignment with the aircraft
air inlet duct system. A lock handle is located in the upper shroud
that secures the Air Inlet Duct in the proper position.
A removable sound attenuator is located inside the Air Inlet Duct, the
attenuator reduces the sound of the air entering the APU.
The engine speed sensors can be accessed by unlocking and
rotating the Air Inlet Duct downward to allow removal of the sound
attenuator. A access cover located on the bottom of the Air Inlet Duct
can be removed to allow inspection of the air intake area and access
to the engine speed sensors.
SPS CT/MAY 1999
Page 4.5
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 4-3. Air Inlet Duct Assembly
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Page 4.6
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
COMBUSTOR ASSEMBLY
COMBUSTOR CHAMBER
The Combustor Assembly consists of the following components:
The annular designed Combustor Chamber is located inside the
combustor housing. Fuel is sprayed into the Chamber and mixed
with compressor impeller air, the fuel air mixture is then ignited by
two ignitors to provide combustion.
Combustor Housing
Combustor Chamber
COMBUSTOR HOUSING
The Combustor Housing is bolted to the air intake housing and
provides the plenum for the combustor chamber. The Housing also
has provisions for a bleed air port, ignitors, start and main fuel
manifolds, start and main fuel nozzles, exhaust thermocouples, and
the anti-surge valve (if installed).
Combustion is a continuous process inside the Chamber where heat
energy is produced to drive the turbine wheel. The inner surface of
the walls are film cooled by air introduced through cooling strips that
are part of the Combustor Chamber.
A combustor drain valve is located on the bottom of the Combustor
Housing and is threaded into the Combustor drain boss. The drain
valve is spring loaded open when the APU is shut down and allows
any residual fuel in the Combustor to flow into the drain system. The
drain valve is closed by Combustor air pressure when the APU is in
operation.
Fuel draining from either the Combustor or the start fuel purge valve
flows into a cleanable filter located inside the filter mount housing,
the fuel then drains overboard through a drain mast located on the
APU compartment access door.
SPS CT/MAY 1999
Page 4.7
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 4-4. Combustor Assembly
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Page 4.8
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
ATTENUATOR ASSEMBLY
The exhaust sound level of the APU is reduced by a sound
Attenuator Assembly that is attached by a v-band clamp to the
combustor housing. The Attenuator directs the exhaust gasses into
the aircraft supplied exhaust duct where the gasses are exhausted
overboard.
Mounted on the exhaust outlet of the Attenuator Assembly is the
eductor extension, the extension is attached by four bolts and can be
adjusted (refer to the Boeing 737 Maintenance Manual) to obtain the
proper eductor gap. The eductor gap between the eductor extension
and the exhaust duct is necessary to provide ambient air cooling of
the exhaust system.
SPS CT/MAY 1999
Page 4.9
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 4-5. Attenuator Assembly
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Page 4.10
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 5
GEARBOX ASSEMBLY
SPS CT/MAY 1999
Page 5.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
The Gearbox Assembly is a one-piece aluminum casting with
mounting pad provisions for the engine assembly and gearbox driven
accessories. The lower part of the gearbox provides the sump for the
oil system.
SPS CT/MAY 1999
Page 5.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 5-1. Gearbox Assembly
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Page 5.2
SUNDSTRAND AEROSPACE
COMPONENTS
GEAR SYSTEM
The internal Gear System provides the necessary speed reduction to
drive the gearbox accessories. The gears are supported by shafts
and bearings that are lubricated by the gearbox oil system.
SPS CT/MAY 1999
Page 5.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 5-2. Gear System
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Page 5.4
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
STARTER MOTOR SHAFT ASSEMBLY
The Starter Motor Shaft Assembly functions as a clutch between the
starter motor and the gearbox assembly and incorporates a splined
shaft, bearings, and a sprag clutch. The clutch is mechanical in
operation and provides automatic engagement and disengagement
of the Shaft Assembly during starter motor operation.
The Starter Motor Shaft Assembly is a replaceable unit and is
secured into the gearbox by a retaining ring, screw, and washer.
SPS CT/MAY 1999
Page 5.5
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 5-3. Starter Motor Shaft Assembly
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Figure 5-4. Sprag Clutch Operation Page 5.6
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 6
LUBRICATION SYSTEM
SPS CT/MAY 1999
Page 6.0
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
The APS 2000 is lubricated by a wet sump oil system that uses the
bottom of the gearbox as the oil sump. The oil system provides a
pressurized supply of oil that lubricates and cools the gears and
bearings in the APU gearbox and rotor assembly
SYSTEM OPERATION
OIL DISTRIBUTION
A positive displacement oil pump provides oil flow to the lubrication
system, the pump is part of the oil pump assembly and is driven by
the gearbox. At the beginning of the APU start sequence the deprime
valve is signaled to open by the FADEC, the open valve prevents the
oil pump from producing oil flow by not allowing the pump to draw oil
from the sump. Preventing oil flow reduces the starter load and
allows faster engine acceleration to operational speed. When 55%
engine speed has been attained, the deprime valve is de-energized
closed and allows the oil pump to produce oil flow to the lubrication
system.
Oil flow from the pump is filtered by a 20 micron replaceable filter
and then cooled by an external oil cooler, the cooler uses air that is
supplied by a cooling fan. The cooled oil then flows through oil
passages in the gearbox to oil jets that provide lubrication and
cooling of the APU gears and bearings. The oil is then returned by
gravity to the oil sump and does not require the use of a scavenge
pump. During lubrication, the oil in the gearbox is turned into an oilair mist and is separated by the rotating action of the generator
gearshaft (oil-air separator) located inside the gearbox. The oil is
returned to the oil sump by gravity and the air is vented through the
generator gearshaft to an external vent tube assembly, the vent tube
is connected to the APU attenuator assembly where the air is vented
into the exhaust.
The oil system pressure is regulated by an oil pressure relief valve.
The valve is set to maintain 45 PSIG. and is non adjustable.
The FADEC monitors the high oil temperature and low oil pressure
switches. If either condition occurs, the APU will automatically shut
down.
The deprime valve is signaled again by the FADEC to open for 30
seconds during shutdown of the APU. This prevents the oil pump
from supplying oil and the oil remaining in the system flows back to
the oil sump by gravity.
SPS CT/MAY 1999
Page 6.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-1. Gearbox Oil Distribution
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Page 6.2
SUNDSTRAND AEROSPACE
SYSTEM OPERATIONS (Continued)
ROTOR BEARING OIL DISTRIBUTION
Lubrication and cooling of the rotor bearings is provided by the
gearbox oil system.
The roller bearing is lubricated by an oil jet located inside the
gearbox assembly, the oil is injected into the hollow quill shaft that is
splined into the coupling ring. The oil flows through passages in the
tie rod and into an area between the tie rod and the hollow rotor
shaft. During engine operation the rotating rotor shaft generates a
centrifugal force on the oil, and forces the oil through passages in the
rotor shaft to lubricate the roller bearing.
Lubrication of the ball bearing is provided by pressurized oil from the
gearbox, the oil flows through a passage in the air intake housing
and into the bearing capsule. The pressurized oil is supplied to the
ball bearing and the squeeze film area by oil passages in the bearing
capsule. The squeeze film oil is used to dampen vibration forces that
may be generated during operation of the APU.
All the oil delivered to the rotor bearings flows out of the bearing
capsule by gravity through oil passages in the bearing capsule and
the air intake housing. The oil is returned to the gearbox oil sump
through a drain hole located in the coupling ring cavity of the gearbox
assembly.
SPS CT/MAY 1999
Page 6.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-2. Rotor Bearing Oil Distribution
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Page 6.4
SUNDSTRAND AEROSPACE
SYSTEM OPERATIONS (Continued)
OIL SEALS
CARBON SEAL DRAIN SYSTEM
Two seals are used in the bearing capsule, a stationary carbon face
seal and a rotating labyrinth seal. The seals prevent oil from entering
the compressor impeller during APU operation.
The Drain System consists of interconnected drain passages
between the bearing capsule, air intake housing and the gearbox
assembly. In the event that oil leaks past the carbon seal, The Drain
System will allow the oil to drain overboard through a drain port
located on the rear face of the gearbox. The Drain System is also
used for venting Labyrinth seal air.
CARBON FACE SEAL
The stationary Carbon Face Seal is pressed into the bearing capsule
and is the primary seal that prevents oil leakage from the capsule.
LABYRINTH SEAL
The rotating Labyrinth Seal is located on the hub of the compressor
impeller, the Seal prevents oil from entering the impeller in the event
of carbon face seal leakage.
Compressor impeller air is used to pressurize the seal, this provides
a none contact seal between the bearing capsule and the Labyrinth
Seal. The air that is used for sealing is then vented back into the
compressor impeller and the carbon seal drain passages.
SPS CT/MAY 1999
Page 6.5
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-3. Oil Seals
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Page 6.6
SUNDSTRAND AEROSPACE
COMPONENTS
OIL PUMP ASSEMBLY
DEPRIME VALVE
The Oil Pump Assembly is a replaceable unit and is mounted on the
front side of the gearbox assembly. The gerotor type Pump is driven
by the gearbox and draws oil from the sump to supply the lubrication
system.
The Deprime Valve is a solenoid operated valve located on the oil
pump assembly. The Valve is controlled by the FADEC and prevents
the oil pump from supplying oil during start up and shut down of the
APU.
OIL FILTER
At start up the valve is energized until 55% engine speed is reached,
this reduces starter motor load and allows faster acceleration of the
engine. At and above 55% engine speed the Valve is de-energized
and allows the oil pump to flow oil into the lubrication system. During
engine shutdown the Valve is again energized for 30 seconds, this
prevents oil flow and allows the oil remaining in the system to drain
back into the oil sump by gravity.
A disposable 20 micron Oil Filter is located inside the oil pump
assembly and filters the oil flowing from the pump. A latching
differential pressure indicator and a relief valve are also provided on
the assembly in the event oil flow through the filter becomes
restricted.
The red latching differential pressure indicator provides a visual
warning when the differential pressure across the Filter reaches 30
to 35 PSID. The indicator can be reset by pressing on the indicator.
The relief valve is set to open at 40 to 45 PSID across the Filter, this
will allow oil to bypass the Filter and maintain oil flow to the system.
OIL PRESSURE RELIEF VALVE
A nonadjustable Oil Pressure Relief Valve is threaded into the lower
rear face of the gearbox assembly. The Valve is replaceable and
regulates the oil pressure between 40 to 45 PSIG.
SPS CT/MAY 1999
Page 6.7
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-4. Oil Pump Assembly–Oil Pressure Relief Valve
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Page 6.8
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
OIL COOLER
The external mounted aluminum Oil Cooler cools the oil flowing from
the oil pump, the oil is then returned to the gearbox oil system. The
Cooler is mounted on a bracket that is secured to the generator, both
the Oil Cooler and the generator use air for cooling that is supplied
by the cooling fan. The air is delivered through a fiber glass cooling
air duct and then exhausts through the lower shroud accessory
cooling air overboard exhaust.
The Oil Cooler incorporates a non adjustable bypass valve that
opens if oil flow through the Cooler becomes restricted. The valve
begins to open when the oil pressure across the Cooler reaches 25
to 35 PSID and is full open at 45 PSID.
SPS CT/MAY 1999
Page 6.9
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-5. Oil Cooler
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Page 6.10
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
COOLING FAN
The Cooling Fan is a replaceable unit and is mounted on the front
face of the gearbox assembly by a V-band clamp. The Fan is driven
by the gearbox and draws ambient air from the aircraft supplied air
inlet duct system. The fan air is then distributed to the oil cooler and
the generator through a fiber glass cooling air duct.
The ball bearings of the Cooling Fan are lubricated and cooled by
the gearbox oil system. A carbon face seal and a labyrinth seal are
used on the Fan shaft to prevent oil from entering the impeller.
The carbon face seal prevents oil leakage from the Cooling Fan
bearing area.
The labyrinth seal prevents oil from entering the impeller in the event
of oil leakage past the carbon face seal. The non contact seal uses
air to pressurize the seal that is supplied from the Cooling Fan scroll
through the external labyrinth seal air line.
SPS CT/MAY 1999
Page 6.11
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-6. Cooling Fan
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Page 6.12
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
OIL PRESSURE SWITCH
OIL LEVEL SENSOR
The remote mounted Oil Pressure Switch is mounted on the rear
face of the oil cooler, the Switch is connected to an oil passage on
the front face of the gearbox assembly by a flexible hose.
The Oil Level Sensor is located on the lower front face of the
gearbox assembly and provides oil level signals to the FADEC. The
signals are used for low oil quantity warning and remote oil servicing.
The remote oil servicing system is an option offered by the aircraft
manufacturer and is not installed on all aircraft.
The Switch is a normally open contact and will close when the oil
pressure reaches 25 PSIG. A decreasing oil pressure of 18 to 22
PSIG will cause the Switch to open. When the APU is started and
reaches 100% engine speed, the FADEC will checks for oil pressure
(switch closed) after 10 seconds. If oil pressure is not present (switch
open), the APU will automatically shut down.
When the APU is running at 100% engine speed for more than 10
seconds (switch closed) and then a loss of oil pressure occurs
(switch open) the APU will automatically shut down in 10 second
after the loss of oil pressure.
HIGH OIL TEMPERATURE SWITCH
High oil temperature is monitored by the High Oil Temperature
Switch that is threaded into the front face of the oil pump assembly.
The Switch contact is normally closed and will open if the oil
temperature reaches 275 ± 5°F and rising, the signal is sent to the
FADEC which initiates an automatic shutdown of the APU after 20
seconds.
SPS CT/MAY 1999
Page 6.13
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-7. Lubrication Switches
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Page 6.14
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
DRAIN PLUG
REMOTE OIL FILL PORT
A Drain Plug is located on the lower front face of the gearbox
assembly, removing the Plug allows the oil to be drained from the oil
sump.
This Port is used when a remote oil servicing system is installed in
the aircraft. The Fill Port is connected by an oil line to the remote oil
service panel, this allows servicing of the oil sump without opening
the APU compartment access door.
The Drain Plug incorporates a magnetic chip detector that is used to
check for ferrous metal that may have entered the oil system. The
chip detector may be removed, inspected and then reinstalled. A
check valve located inside the Drain Plug prevents the loss of oil
when the chip detector is removed.
OIL SIGHT GLASS
The oil level in the sump can be checked by using the Sight Glass
located on the lower front face of the gearbox assembly. The Glass
provides a visual indication of the oil level and is marked ADD and
FULL.
OIL FILL TUBE
Oil servicing of the APU can be accomplished by opening the APU
compartment door and removing the filler port cover located on the
left side of the lower shroud. The port allows access through the
lower shroud to the APU Oil Fill Tube. The Fill Tube has a locking
cap with a dipstick attached that is marked with ADD and FULL,
unlocking and removing the cap allows servicing of the oil sump. A
hole located in the Fill Tube prevents over filling of the oil sump and
allows the excess oil to exit through the lower shroud drain system.
It is important the Oil Fill Tube cap is reinstalled and properly locked
in place to prevent excessive loss of oil during operation of the APU.
SPS CT/MAY 1999
Page 6.15
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-8. Oil Servicing
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Page 6.16
SUNDSTRAND AEROSPACE
INTERFACE
REMOTE OIL SERVICING
On some aircraft an optional Remote Oil Service Panel is installed to
provide oil servicing of the APU. The Service Panel is located on the
lower side of the tail section, just forward of the APU compartment
access door.
Electrical power is provided to the Service Panel when the door is
open, this allows an amber ADD light to illuminate if the oil level is
low or a green FULL light to illuminate if the oil level is full.
Oil servicing is accomplished by connecting an oil service unit to the
pressure fill connection on the service panel, when the green FULL
light illuminates the oil servicing will automatically shut off to prevent
over filling of the oil sump.
SPS CT/MAY 1999
Page 6.17
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 6-9. Remote Oil Servicing
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Page 6.18
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 7
PNEUMATIC SYSTEM
SPS CT/MAY 1999
Page 7.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
The APU provides compressed bleed air to the aircraft pneumatic
systems when it is required. The air is used for main engine starting,
air conditioning and other aircraft pneumatic system requirements.
Ambient air is needed to operate the APU, the air is delivered
through an air inlet duct system that is part of the aircraft tail section.
The air inlet door located at the inlet to the duct is required to be
open for the APU to operate. The door is controlled by the FADEC
and allows ambient air to supply the APU cooling fan and the
compressor impeller.
The exhaust duct extends through the tail section to allow the APU
exhaust gasses to exit overboard, it is also provided with a sound
attenuating material that reduces the sound level of the exhaust.
SPS CT/MAY 1999
Page 7.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 7-1. APU Air Supply
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Page 7.2
SUNDSTRAND AEROSPACE
SYSTEM OPERATION
Ambient air enters the air inlet duct where the air is directed to the
APU cooling fan and the air inlet housing. The cooling fan air is used
for cooling by the APU oil cooler and the generator.
The air entering the air inlet housing is used by the compressor
impeller to operate the APU and provide compressed air to the
aircraft pneumatic systems. The air is heated by compression and
flows into the APU bleed air duct where the air is used to open the
cooling air shutoff valve and provide the fuel heater with hot air.
Located at the end of the bleed air duct is the aircraft supplied bleed
air valve, the valve controls airflow delivery from the APU to the
aircraft pneumatic systems. The valve is opened and closed by the
APU bleed switch on the flight deck bleed control panel. When the
bleed air valve is open, the valve can be modulated automatically to
allow maximum airflow delivery with out exceeding the APU exhaust
gas temperature limits. Modulation of the bleed air valve is
accomplished by the bleed servo valve using signals from the
FADEC.
The anti-surge valve is only used on the early models of the APU.
The valve is mounted on the bottom side of the combustor housing
and is open to prevent possible compressor impeller surge by the
FADEC when the APU is operating at altitudes above 25,000 ft.
SPS CT/MAY 1999
Page 7.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 7-2. Bleed Air System
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Page 7.4
SUNDSTRAND AEROSPACE
COMPONENTS
BLEED SERVO VALVE
The Bleed Servo Valve is mounted on a bracket that is located on
the left side of the engine, the Valve controls the modulation of the
bleed air valve by using signals from the FADEC. The FADEC
receives millivolt signals from the APU exhaust thermocouples and
converts the signals into milliamp signals, the milliamp signals are
used to operate the Servo valve.
The Servo Valve is open ( no signal from the FADEC) at start up, this
prevents the bleed air valve from opening before the APU reaches
100% engine speed.
When 100% engine speed is reached, the FADEC signals the Servo
Valve to close. Air pressure is trapped in the control chamber of the
bleed air valve and causes the valve to open; providing the APU
bleed switch is turned ON.
During bleed air operation an increase in APU exhaust gas
temperature will occur. The exhaust gas temperature is maintained
within limits by the Bleed Servo Valve. The Valve meters and vents
air pressure from the bleed air valve control chamber to modulate the
bleed valve.
Modulating of the bleed air valve allows maximum air flow delivery
with out exceeding the APU exhaust gas temperature limits.
SPS CT/MAY 1999
Page 7.5
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 7-3. Bleed Servo Valve
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Page 7.6
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
ANTI-SURGE VALVE
The Anti-Surge Valve is located on the bottom side of the combustor
housing and is installed on the early model APU's.
The electro-pneumatic valve is normally closed and requires air
pressure and a signal from the FADEC to open. The Valve is open
when the APU is operating at altitudes of 25,000 feet and above, this
allows combustor air pressure to vent overboard and prevent the
possibility of compressor impeller surge.
SPS CT/MAY 1999
Page 7.7
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 7-4. Anti-Surge Valve
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Page 7.8
SUNDSTRAND AEROSPACE
INTERFACE
AIRCRAFT PNEUMATIC SYSTEM
The Aircraft Pneumatic System can be supplied with bleed air from
the main engines or the APU, bleed air is available from the APU
during ground or in-flight operation.
FLIGHT DECK BLEED CONTROL PANEL
Control of the pneumatic system is provided by switches located on
the Bleed Control Panel. Selecting the APU bleed switch to ON
opens the bleed air valve and allows the APU to supply the
pneumatic system with air.
SPS CT/MAY 1999
Page 7.9
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 7-5. Aircraft Pneumatic System
Figure 7-6. Flight Deck Bleed Control Panel
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Page 7.10
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 8
FUEL SYSTEM
SPS CT/MAY 1999
Page 8.0
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SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
Fuel is supplied to the APU electronic fuel control and pump
assembly (Fuel Control) from the aircraft fuel system, the fuel is
metered by the Fuel Control using signals from the FADEC.
OPERATION
The Fuel Control is driven by the gearbox assembly that operates
two internal fuel pumps, a centrifugal pump and a high pressure
pump. Both pumps are mounted on a common shaft.
remaining fuel for 60 seconds and then the valve is signaled to close.
Purging occurs again for 30 seconds during shut down of the APU.
During engine acceleration, the servo valve and the main fuel valve
are signaled to open when the FADEC senses a rise in APU exhaust
gas temperature and 5% engine speed. Both valves remain open
during acceleration and constant speed operation.
The centrifugal pump draws fuel from the aircraft fuel system, the
fuel is then pumped through an external fuel filter and then back to
the high pressure pump.
Constant speed operation of the APU is maintained at 100% engine
speed during all load conditions. The servo valve meters the required
fuel flow to fourteen main nozzles, the nozzles spray fuel into the
combustor chamber to maintain combustion. Fuel metering of the
servo valve is controlled by milliamp signals provided by the FADEC.
The high-pressure pump provides fuel to the system and the
pressure is regulated by a relief valve. Fuel is distributed internally to
the following components: servo valve, main fuel valve, start fuel
valve and the differential pressure valve. The differential pressure
valve is located inside the Fuel Control and maintains a constant fuel
differential pressure across the servo valve for fuel metering
purposes.
The APU is normally shut down when the FADEC de-energizes the
main fuel valve closed, fuel to the main nozzles is turned off and the
combustion process ceases. During this time, the FADEC maintains
an open signal to the servo valve for 1 second and then deenergizes the valve closed. If the engine speed has not decreased
below 95% during the 1 second time limit, the FADEC will
annunciate MFVL (main fuel valve).
Fuel delivery to the engine is provided by the Fuel Control using
signals from the FADEC. The signals allow the Fuel Control to
deliver the required fuel for starting, acceleration and maintaining
constant engine speed. The Fuel Control also provides normal and
fault shut down of the APU using signals from the FADEC.
The FADEC annunciation of MFVL indicates the main fuel valve has
remained open and shut down of the APU is being accomplished by
the servo valve.
At start up, fuel is delivered to the engine by the Fuel Control when
the start fuel valve is signaled to open at 2% engine speed. Fuel is
sprayed into the combustor chamber by four start nozzles and
ignited by the ignition system. The start fuel valve remains open until
70% engine speed is reached, at this time the FADEC signals the
valve to close and the start purge valve to open. The open purge
valve allows combustor air pressure to purge the start nozzles of any
The Fuel Pump Drive Spline is lubricated with oil provided by the
gearbox lubrication system. A preformed packing is installed on the
drive spline to prevent oil leaking into the fuel pump shaft seal drain.
Excessive oil loss will occur if the packing is damaged or not
installed.
FUEL PUMP DRIVE SPLINE
SPS CT/MAY 1999
Page 8.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 8-1. Fuel System
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Page 8.2
SUNDSTRAND AEROSPACE
COMPONENTS
FUEL FILTER ASSEMBLY
The external Fuel Filter Assembly is located on the left side of the
APU and filters fuel to the high pressure pump in the fuel control.
The Filter Assembly uses a full flow 10-micron replaceable filter
element, it also incorporates a filter bowl lock, a latching differential
pressure indicator and a bypass valve.
The differential pressure indicator provides a visual warning that fuel
flow through the filter has become restricted. The indicator will
appear when the differential pressure across the filter reaches 6
PSID.
The bypass valve will open when fuel flow through the filter is
restricted to cause a differential pressure across the filter of 10 PSID.
The open bypass valve provides an unrestricted flow of fuel through
the Fuel Filter Assembly to allow normal operation of the APU. If this
condition occurs, a minimum amount of fuel will be filtered.
SPS CT/MAY 1999
Page 8.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 8-2. Fuel Filter Assembly
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Page 8.4
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
MAIN FUEL CHECK VALVE
START PURGE VALVE
The Main Fuel Check Valve is installed in the main fuel line between
the fuel control and the main nozzles. The Check Valve is used to
prevent fuel from draining out of the fuel line during shutdown of the
APU. The fuel remaining in the line is used to provide a positive fuel
supply to the main nozzles during the next APU start sequence.
The Start Purge Valve is controlled by the FADEC and is located in
the start fuel line between the fuel control and the start nozzles. The
FADEC signals the Purge Valve to open when 70% engine speed is
reached. The open Purge Valve allows combustor air pressure to
purge the start nozzles of any remaining fuel for 60 seconds and
then is signaled to close. Purging again occurs for 30 seconds during
shut down of the APU.
Located at the inlet to the Main Fuel Check Valve is a reducer fitting,
the fitting incorporates a 150 micron filter and functions as a last
chance filter. On later production models the filter has been deleted
from the fitting.
Air purging of the start fuel system prevents any residual fuel from
forming carbon deposits on the start nozzles during operation of the
APU. The fuel is removed through the open Start Purge Valve and
into the APU drain system.
SPS CT/MAY 1999
Page 8.5
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 8-3. Main Fuel Check Valve
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Figure 8-4. Start Purge Valve
Page 8.6
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
START FUEL MANIFOLD
MAIN FUEL MANIFOLD
Flexible tubing is also used for the Start Fuel Manifold that is located
on the combustor housing. The Manifold delivers start fuel from the
fuel control to the four start nozzles.
The Main Fuel Manifold is a flexible tubing located around the
combustor housing. The Manifold receives metered fuel from the fuel
control and distributes the fuel to the main nozzles.
START NOZZLES
MAIN NOZZLES
There are four start nozzles located on the combustor housing, two
on the left side and two on the right side. The nozzles extend into the
combustor chamber near the igniters, the atomized fuel produced by
the the start nozzles is ignited by the ignition system during the APU
start sequence.
There are fourteen individual Main Nozzles located around the
combustor housing. The Nozzles extend into the combustor chamber
where combustor air is used by the Nozzles to atomize the fuel. The
atomized fuel is then burned in the combustor chamber to maintain
engine operation.
SPS CT/MAY 1999
Page 8.7
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 8-5. Start Fuel Manifold and Nozzles
Figure 8-6. Main Fuel Manifold and Nozzles Page 8.8
Use or disclosure of this data is subject to the
restriction on the title page of this document.
SUNDSTRAND AEROSPACE
INTERFACE
AIRCRAFT FUEL SYSTEM
APU fuel is normally supplied from tank no. 1 by the AC boost
pumps, or suction feed by the APU fuel control pump. Fuel is
available from any of the other fuel tanks with appropriate use of the
AC boost pumps and the cross feed valve. (An optional DC boost
pump may be installed to provide fuel to the APU from tank no. 1)
The APU fuel shutoff valve is an electric motor driven gate valve with
a manual override handle and is located in the left wheel well on the
rear wing spar. The open and closing of the valve is controlled by
signals from the FADEC. Fuel supply to the APU requires the valve
to be in the open position.
SPS CT/MAY 1999
Page 8.9
Use or disclosure of this data is subject to the
restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 8-7. Aircraft Fuel System
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 8.10
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 9
ELECTRICAL SYSTEM
SPS CT/MAY 1999
Page 9.0
Use or disclosure of this data is subject to the
restriction on the title page of this document.
SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
The APU Electrical system is controlled by the APU Control Unit
(APUCU) and the Full Authority Digital Electronic Controller
(FADEC), the two units working together along with signals from
other components control the starting, acceleration, running and
shutdown of the APU
COMPONENTS
STARTER MOTOR
The Starter Motor is located on the lower front side of the gearbox
assembly and is powered by the aircraft battery. Power to the Starter
Motor is provided when the APU start command is initiated, the
Motor remains powered until 55% engine speed has been attained.
At this time, the Motor is de-energized and the APU accelerates to
100% engine speed.
Located on the front of the Starter Motor is a connector that provides
excessive brush wear and low voltage signals to the FADEC.
EXCITER
The Exciter is a capacitor-discharge unit that uses DC power to
produce an intermittent high voltage output to the igniters. Energizing
of the Exciter occurs when the APU start command is initiated and
2% engine speed is attained. The Exciter continues to provide high
voltage output and then is de-energized at 55% engine speed.
WARNING
THE EXCITER PROVIDES HIGH VOLTAGE
OUTPUTS AND CAN BE DANGEROUS. WHEN
REPLACING THE IGNITION EXCITER, BE SURE
ELECTRICAL POWER IS REMOVED FROM THE
EXCITER FOR A MINIMUM OF FIVE (5) MINUTES.
DISCONNECT IGNITER CABLES FROM IGNITER
PLUGS. DISCHARGE THE EXCITER BY
TOUCHING THE IGNITER CABLE ENDS TO THE
IGNITER PLUG SHELL. BE SURE EXCITER IS
FULLY DISCHARGED BEFORE REMOVING THE
IGNITER CABLES AND EXCITER.
IGNITERS
There are two igniters threaded into the combustor housing, one on
the left side and one on the right side. The Igniters extend into the
combustor chamber where they ignite the fuel delivered by the start
nozzles.
Two separate ignition cables are used to deliver high voltage from
the exciter to each Igniter.
SPS CT/MAY 1999
Page 9.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 9-1. Starter Motor
Figure 9-2. Ignition System
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 9.2
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
EVENT MONITORING UNIT
ENGINE SERIAL NUMBER ASSEMBLY
The Event Monitoring Unit is mounted on a bracket located below the
cooling air duct assembly, the Unit houses the hour meter, start
counter and a resistive temperature detector. The hour meter and
start counter are operated by the FADEC. The resistive temperature
detector provides cold junction compensation for the exhaust
thermocouple signals that are sent to the FADEC, it also provides
the FADEC with ambient temperature information from inside the
APU compartment shroud. The ambient temperature information is
used by the FADEC to establish the APU exhaust gas temperature
shutdown limit.
The Engine Serial Number Assembly is located on the left side of the
APU. The Assembly consists of a connector, printed circuit board
and protective covers for the circuit board. The engine identification
number is programmed into the circuit board, the number is sent to
the FADEC and stored during power-up initialization of the APU.
The stored Engine Serial Number is used to identify the APU engine
number with the data that is provided by the FADEC.
SPS CT/MAY 1999
Page 9.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 9-3. Event Monitoring Unit
Figure 9-4. Engine Serial Number Assembly
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restriction on the title page of this document.
Page 9.4
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
THERMOCOUPLES
SPEED SENSORS
There are two Thermocouples located on each side of the combustor
housing exhaust flange. The thermocouples extend into the exhaust
gas stream and provide a temperature signal to the FADEC and the
flight deck exhaust temperature indicator.
There are two Speed Sensors located inside the air inlet duct and
mounted on the air intake housing. The magnetic probe of each
Speed Sensor extends through the air intake housing and align with
the rotating coupling ring located on the end of the rotor assembly.
Each time a lobe on the rotating coupling ring passes the magnetic
probes a speed signal is sent to the FADEC, the signals are used for
rotor speed sensing. The Speed Sensors are independent of each
other in operation, they allow the APU to continue to run in the event
that one of the Speed Sensors becomes inoperative.
Each Thermocouple is independent of each other in operation, they
allow the APU to continue to run in the event that one of the
thermocouples becomes inoperative.
A preformed packing is required between the Speed Sensor and the
air intake housing. If the packing is not installed, excessive loss of
engine oil will occur.
SPS CT/MAY 1999
Page 9.5
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 9-5. Thermocouple
Figure 9-6. Speed Sensor
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 9.6
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
PRESSURE TRANSDUCER
AMBIENT TEMPERATURE SENSOR
The Pressure Transducer is mounted on the top left side of the APU
air inlet duct. The Transducer senses ambient air pressure inside the
air inlet duct and sends the pressure signals to the FADEC. The
FADEC uses the signals to provide the fuel control with altitude
compensation and control of the anti-surge valve. (The surge valve is
only used on the early models of the APU).
The Ambient Temperature Sensor is mounted just below the
pressure transducer. The Sensor probe extends into the air inlet duct
and sends ambient temperature signals to the FADEC. The FADEC
uses the signals to provide the fuel control with ambient temperature
compensation and to establish the APU exhaust gas temperature set
point. The set point is used by the FADEC to control the bleed servo
valve, the servo valve will cause a reduction in bleed airflow in the
event the exhaust gas temperature becomes excessive.
The FADEC also uses the Ambient Temperature sensor signals to
shut down the APU if the air inlet duct air temperature exceeds
250°F for 10 seconds.
The high air temperature can be caused by the main engines back
pressuring the APU with hot, high pressure air. The APU is shut
down to prevent damage to the APU during bleed air operation.
SPS CT/MAY 1999
Page 9.7
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 9-7. Pressure Transducer
Figure 9-8. Ambient Temperature Sensor
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restriction on the title page of this document.
Page 9.8
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
APU CONTROL UNIT
The APU Control Unit (APUCU) is located in the aircraft electronic
equipment bay and electrically interfaces between the aircraft
electrical system and the FULL Authority Digital Electronic Controller
(FADEC). The circuit breaker located on the front of the APUCU
provides circuit protection for the internal components and electrical
power to the FADEC.
The opening and closing of the APU air inlet door and the APU fuel
shutoff valve is also controlled by signals from the APUCU.
SPS CT/MAY 1999
Page 9.9
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 9-9. APU Control Unit
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Page 9.10
SUNDSTRAND AEROSPACE
COMPONENTS (Continued)
FULL AUTHORITY DIGITAL ELECTRONIC CONTROLLER
The operation of the APU is electronically controlled by the Full
Authority Digital Electronic Controller (FADEC) and is located inside
the aircraft aft cargo compartment, near the cargo door.
On the front face of the FADEC is a Fault Code Label, Scrolling
Label, Fault Display Switch, Fault Display Window and Electrical
Connector (J-l).
FAULT CODE LABEL - Is used to decipher the coded messages that
appear in the fault display window.
SCROLLING LABEL - Provides instructions for scrolling the coded
messages that appear in the fault display window.
FAULT DISPLAY SWITCH - Pushing the Switch will scroll the coded
messages for each of the last twelve APU run cycles.
FAULT DISPLAY WINDOW - The Window displays the coded
maintenance and fault messages by using four light emitting diodes.
ELECTRICAL CONNECTOR (J-l) - The connector is provided to
allow down loading of maintenance and fault data that is stored in
the memory of the FADEC. Down loading may be accomplished by
using a laptop computer and a special cable assembly, the cable
assembly interfaces between the laptop computer and the FADEC.
SPS CT/MAY 1999
Page 9.11
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 9-10. Full Authority Digital Electronic Controller
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 9.12
SUNDSTRAND AEROSPACE
INTERFACE
APU START SWITCH
APU INDICATORS
The APU Start Switch is located on the flight deck overhead panel
and has three positions: Off, On and Start. The Start position is a
momentary selection, when the Switch is released it will return to the
On position.
APU Indicators are also provided on the flight deck overhead panel,
they consist of Warning Lights, Exhaust Temperature and AC
Amperes.
WARNING LIGHTS
OFF - Shuts down the APU, closes the APU fuel shutoff valve and
the air inlet door.
MAINT (Blue) - The APU requires maintenance attention.
ON - Powers up the APU, opens the APU fuel shutoff valve and the
air inlet door.
OIL PRESSURE (Amber) - The APU has shutdown due to a loss of
oil pressure.
START - Energizes the starter motor after all the APU start
requirements have been completed.
FAULT (Amber) - The APU has shutdown due to a fault condition.
OVERSPEED (Amber) - The APU has shutdown due an overspeed
condition.
EXH TEMP - Displays the APU exhaust gas temperature in °C when
the APU is operating.
AC AMPERES - Displays the APU generator load in Amperes when
the generator is connected to the aircraft bus system.
SPS CT/MAY 1999
Page 9.13
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 9-11. APU Start Switch
Figure 9-12. APU Indicators
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restriction on the title page of this document.
Page 9.14
SUNDSTRAND AEROSPACE
INTERFACE (Continued)
APU GENERATOR
APU GENERATOR SWITCHES
The AC Generator is mounted on the front face of the gearbox
assembly. The air cooled, 400 Hz, 115/200 volt generator is rated at
111 Amperes (40 KVA). During ground operation of the APU, the
generator can supply all the aircraft electrical buses to a maximum of
165 Amperes (60 KVA). The increase load on the generator during
ground operation is allowed due to the cooling air provided by the
APU cooling fan.
There are two Generator Switches located on the flight deck
overhead panel. Each is a three-position switch, momentary ONOFF and spring loaded to the center position.
ON-Connects the APU generator to the aircraft bus system.
OFF- Disconnects the APU generator from the aircraft bus system.
SPS CT/MAY 1999
Page 9.15
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999 Figure 9-13. APU Generator
Figure 9-14. APU Generator Switches
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 9.16
SUNDSTRAND AEROSPACE
INTERFACE (Continued)
APU FIRE PROTECTION
GROUND CONTROL PANEL
Fire detection and extinguishing systems are provided by the aircraft
manufacturer for the APU. In the event the detection system senses
a fire, the APU will automatically shutdown, red fire warning lights
illuminate (flight deck and the right wheel well) and a bell sounds in
the flight deck. When the aircraft is on the ground a horn is also
activated in the right wheel well.
FIRE WARNING LIGHT AND HORN - When a fire is detected on the
ground, the Light and Horn will operate.
The APU can be shut down and the fire extinguisher bottle
discharged from either the flight deck Fire Control Panel or the
Ground Control Panel located in the right wheel well.
HORN CUTOUT SWITCH - Pushing the Switch silences the warning
horn.
FIRE CONTROL HANDLE - When the Fire Control Handle is pulled
down, the handle shuts the APU down, arms the fire extinguisher
bottle, closes the APU fuel shutoff valve and the air inlet door.
BOTTLE DISCHARGE SWITCH - Selecting the Switch will discharge
the fire extinguisher bottle.
FIRE CONTROL PANEL
APU FIRE CONTROL HANDLE - A red light illuminated in the
Handle indicates a fire in the APU. When pulled up, the Handle shuts
the APU down, arms the fire extinguisher bottle, closes the APU fuel
shutoff valve and the air inlet door. Rotating the Fire Control Handle
will then discharge the fire extinguisher bottle into the APU
compartment shroud.
APU BOTTLE DISCHARGED - This amber light located on the Fire
Control Panel indicates the APU fire extinguisher bottle has been
discharged.
SPS CT/MAY 1999
Page 9.17
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
Figure 9-15. Fire Control Panel
SPS CT/MAY 1999
Figure 9-16. Ground Control Panel
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 9.18
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 10
START/STOP SEQUENCES
SPS CT/MAY 1999
Page 10.0
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 10-1. Start Sequence
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 10.1
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 10-2. Stop Sequence
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 10.2
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 11
LINE REPLACEABLE UNITS
SPS CT/MAY 1999
Page 11.0
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
COMPONENTS
The following components are categorized as line replaceable units (LRU’s) that can be removed and replaced without removing the APU from the
aircraft. The aircraft maintenance manuals provide removal and installation procedures.
APU Control Unit (not shown)
FADEC (not shown)
Engine Harness
Starter Motor
Cooling Fan
Oil Cooler (not shown)
Fuel Control
Exciter
Event Monitoring Unit (not shown)
Engine Serial Number Assembly
Ambient Temperature Sensor
Ambient Pressure Transducer
Speed Sensors
Thermocouples
High Oil Temperature Switch
Oil Pressure Switch
Oil Pressure Relief Valve
Oil Level Sensor
Igniters
*
*
Ignition Cables
Start Purge Valve
Bleed Servo Valve
Anti-Surge Valve
Combustor Drain Valve
Main Fuel Check Valve
Reducer Fitting (Filter)
De-prime Valve
Oil Pump Assembly
Oil Filter
Fuel Filter Assembly
Fuel Filter Element
Magnetic Drain Plug
Starter Motor Shaft Assembly
Gear Box Vent Flame Arrestor
Main Nozzle
Start Nozzle
Drain Filter
Misc. Tubes/Ducting
*
Eight of the fourteen main nozzles are accessible with the APU installed in the aircraft.
*
Three of the start nozzle assemblies are accessible with the APU installed in the aircraft.
SPS CT/MAY 1999
Page 11.1
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 11-1. Front View
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Page 11.2
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figrue 11-2. Left Side View
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restriction on the title page of this document.
Page 11.3
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 11-3. Right Side View
Use or disclosure of this data is subject to the
restriction on the title page of this document.
Page 11.4
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 11-4. Rear View
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restriction on the title page of this document.
Page 11.5
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 12
MAINTENANCE INSPECTIONS
SPS CT/MAY 1999
Page 12.0
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
GENERAL DESCRIPTION
INSPECTION CHECKS
BORESCOPE INSPECTION
VISUAL INSPECTION
The following components of the turbine assembly may be inspected
by use of the borescope:
Removing the APU lower shroud for corrective maintenance or
servicing provides the opportunity to visually inspect the APU for
security, leaks, and warning indicators. The following are
recommended inspection items:
Turbine Blade Tips
Combustor Chamber
Engine Mounts
Turbine Nozzle Vanes
Engine Components and Fluid Lines
Turbine Wheel Blades
Oil Quantity and Magnetic Drain Plug
Compressor Impeller Blades
Oil and Fuel Filter Bypass Indicators
Diffuser
Electrical Harness and Connectors
Engine Air Inlet Duct
Engine Combustor Housing and Exhaust System
SPS CT/MAY 1999
Page 12.1
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 12-1. APU Borescope Inspection Points
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restriction on the title page of this document.
Page 12.2
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 13
FAULT ISOLATION
SPS CT/MAY 1999
Page 13.0
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
FAULT ISOLATION
FAULT INFORMATION
In the event a maintenance or fault condition occurs with the APU,
the Full Authority Digital Electronic Controller (FADEC) provides
coded information that may be used in trouble shooting. This
information is presented in the Fault Display Window on the front
face the FADEC.
The Fault Display Switch is located above the Fault Display Window
and is used to scroll the maintenance and fault messages of the last
twelve APU run cycles. To use the scrolling feature, the APU start
switch must be Off and the Fault Display Switch pushed. Scrolling
will then commence with the following information appearing in the
Fault Display Window.
The first display will be ENID (Engine Number Identification) followed
by the second display showing the engine number 307 (example).
The third display will show HIST (Run Cycle History) and then the
fourth display provides the Last run message (RN12).
The Run Cycle History is scrolled in a reverse chronological order
until END is displayed. The FADEC will then return to the Last run
message (RN12) for two minutes before the display light goes out.
Maintenance and fault Run messages will always be displayed in
order of severity. Fault message will be displayed ahead of the
maintenance message when both occur in the same run cycle.
Example:
ENID
307
HIST
Last run message (RN12)
RN11
Run message
RN10
Run Message
RN9
Run Message
RN8
Run Message
RN7
Run Message
RN6
Run message
RN5
Run message
RN4
Run message
RN3
Run Message
RN2
Run Message
RN1
Run Message
END
When no maintenance or fault message exists with respect to each
run cycle, the Run message "OK" will be displayed. In some
instances during scrolling when less than twelve run cycles have
occured, the Run message "N/A" (Not Applicable) will be displayed.
To repeat the scolling process, push the Fault Display Switch again
after the FADEC returns to the Last run message(RN12) and the
display light goes out.
SPS CT/MAY 1999
Page 13.1
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
FAULT ISOLATION (Continued)
ACCL FAIL TO ACCELERATE
DISPLAY CODES
The FADEC monitors the operation of the APU and will provide
coded maintenance and fault messages in the Fault Display Window
in the event of a malfunction.
The acceleration of the APU is less than 0.125% per second
for ten seconds after light off or there is a deceleration of 5%
or more for three seconds.
The following information provides the coded messages that can be
displayed by the FADEC, the cause of the malfunction, and the Flight
Deck indication.
Flight Deck Indication: FAULT light
ACFT AIRCRAFT FAULT
1. The “APU” fire switch is pulled.
2. The remote fire switch is pulled.
3. An APU fire is detected.
4. The air inlet door is fully open when the APU master
switch is moved to the ON position.
5. The air inlet door is not fully open thirty seconds after the
APU master switch is moved back to the START
position.
6. The “BAT” switch is moved to the OFF position. (Ground
only)
7. APU air inlet air temperature exceeds 250°F for ten
seconds due to pneumatic back pressure of the APU
from the main engines.
Flight Deck indication: FAULT light
SPS CT/MAY 1999 Figure 13-1. FADEC Fault Code Label
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Page 13.2
SUNDSTRAND AEROSPACE
FAULT ISOLATION (Continued)
DISPLAY CODES (Continued)
BLD
ACFT AIRCRAFT FAULT
BLEED ENABLE
There is a short circuit in the bleed enable system. The
system included the Miscellaneous Switching Module (M278) located in the aircraft E-3 bay. The M-278 module is
supplied by Boeing.
There is an open or short in the ready to load circuit between
the FADEC and the APUCU (bleed air and generator
inoperative)
Flight Deck indication: None
Flight Deck indication: None
AMBP AMBIENT PRESSURE TRANSDUCER
ECU
ELECTRONIC CONTROL UNIT (FADEC)
There is an open or short in the ambient pressure sensing
system.
There is a fault internal to the FADEC.
Flight Deck indication: None
Flight Deck indication: FAULT
AMBT AMBIENT TEMPERATURE SENSOR
There is a maintenance fault internal to the FADEC.
Flight Deck indication: None
There is an open or short in the ambient temperature
sensing system.
EMU
EVENT MONITORING UNIT
Flight Deck indication: None
1. There is an open or short circuit in the cold junction
circuit.
ASVL ANTI-SURGE VALVE
There is an open or short in the anti-surge valve system.
2. There is a short in the start counter circuit.
Flight Deck indication: None
3. There is a short in the hourmeter circuit.
Flight Deck indication: None
SPS CT/MAY 1999
Page 13.3
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restriction on the title page of this document.
SUNDSTRAND AEROSPACE
FAULT ISOLATION (Continued)
DISPLAY CODES (Continued)
LITE
EXCT EXCITER
FAIL TO LIGHTOFF
There is an open or short circuit in the primary side of the
exciter circuit.
The EGT did not rise within six seconds after 2% speed was
reached.
Flight Deck indication: None
Flight Deck indication: FAULT light
LOP
FSRV FUEL SERVOVALVE
LOW OIL PRESSURE
The circuit for low oil pressure is open after the APU has
reached 100% speed. When this condition persists for more
than ten seconds, the APU shuts down.
There is an open or short circuit in the main fuel servovalve
system.
Flight Deck indication: None
Flight Deck indication: LOP light
GDOV GEARBOX DE-OILING VALVE
LOQ
There is an open or short circuit in the gearbox de-oiling
valve system.
HOT
LOW OIL QUANTITY
Flight Deck indication: None
The circuit for low oil quantity is open (the oil quantity switch
opens when the sump is approximately 1 quart below the
FULL mark on the sight glass).
HIGH OIL TEMPERATURE
Flight Deck indication: MAINT light
The circuit for high oil temperature opened for twenty
seconds (the oil temperature switch opens at 275°F and
rising)
When low oil quantity is sensed during APU start up, the
blue MAINT light illuminates and remains illuminated during
operation of the APU.
Flight Deck indication: FAULT light
Page 13.4
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SUNDSTRAND AEROSPACE
FAULT ISOLATION (Continued)
DISPLAY CODES (Continued)
OVSP OVERSPEED
MFVL MAIN FUEL VALVE
1. There is an open or short circuit in the main fuel valve
system.
The APU rotor speed has exceeded 105% speed.
When APU overspeed occurs, the APU will shutdown but the
FADEC will not display OVSP on the fault indicator. For the
FADEC to display OVSP, it is necessary to position the APU
switch to OFF and wait 5 minutes for the FADEC to power
down. Pushing the fault display switch will then annunciate
OVSP on the fault indicator display.
Flight Deck indication: None (open circuit)
FAULT (short circuit)
2. Main fuel valve mechanically failed open.
Flight Deck indication: MAINT light
The APU cannot be restarted until the APU switch has been
positioned to OFF for 5 minutes.
OPSW OIL PRESSURE SWITCH
The circuit for the oil pressure switch is grounded and is
detected in the start preparation phase prior to engaging the
starter. The fault will not be detected when the APU begins
to start.
Flight Deck indication: OVERSPEED light
PWRF POWER FAILURE
The 28V DC power supplied to the FADEC has decreased
below 10.5 volts.
Flight Deck indication: FAULT light
OTMP OVERTEMPERATURE
Flight Deck indication: FAULT light
Exhaust Gas Temperature limit exceeded when the APU is
operating at 100% engine speed.
SFVL
START FUEL VALVE
There is an open or short circuit in the start fuel valve
system.
Flight Deck indication: FAULT Light
OTST OVERTEMPERATURE AT START
Flight Deck indication: None
Exhaust Gas Temperature limit exceeded during APU start
and acceleration.
Flight Deck indication: FAULT Light
Page 13.5
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SUNDSTRAND AEROSPACE
FAULT ISOLATION (Continued)
DISPLAY CODES (Continued)
SPD1
SRVB BLEED SERVOVALVE
SPEED #1
There is an open or short circuit in the #1 speed sensing
system.
There is an open or short circuit in the bleed servovalve
system.
Flight Deck indication: MAINT light (and FAULT light if SPD2
has also failed).
Flight Deck indication: None
STRT STARTER FAILURE OR WARNING
SPD2
SPEED #2
1. APU speed greater than 10% at start.
There is an open or short circuit in the #2 speed sensing
system.
Flight Deck indication: MAINT light (and FAULT light if SPD1
has also failed).
SPVL
START PURGE VALVE
3. Exhaust Gas Temperature rise prior to start.
4. The starter brush wear switch is open due to the brushes
exceeding wear limits.
There is an open or short circuit in the start fuel purge
system.
Flight Deck indication: None
2. APU speed less than 5% at fifteen seconds after starter
engagement or light off.
5. The starter voltage is less than six volts during start.
Flight Deck indication: FAULT light
(conditions 1, 2, 3)
Flight Deck indication: None
(conditions 4, 5)
SPS CT/MAY 1999
Page 13.6
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SUNDSTRAND AEROSPACE
FAULT ISOLATION (Continued)
DISPLAY CODES (Continued)
TC1
THERMOCOUPLE #1
There is an open or shut circuit detected in the #1
thermocouple system.
Flight Deck indication: MAINT light (and FAULT light if TC2
has also failed).
TC2
THERMOCOUPLE #2
There is an open or short circuit detected in the #2
thermocouple system.
Flight Deck indication: MAINT light (and FAULT light if TC1
has also failed).
UNSP UNDERSPEED
The rotor speed of the APU has decreased to 97% from
100% speed.
Flight Deck indication: FAULT light
NOTE: Refer to the Boeing 737
Maintenance Manual –
Troubleshooting Chapter
49-00-00 for troubleshooting
procedures.
SPS CT/MAY 1999
Page 13.7
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SUNDSTRAND AEROSPACE
FLIGHT DECK INDICATORS
A fault condition will cause the blue MAINT. light, amber LOW OIL
PRESSURE, FAULT or OVERSPEED light to illuminate. The light
will remain illuminated as long as the APU switch remains in the ON
position. All indicator lights will extinguish when the APU switch is
placed in the OFF position except main fuel valve (mechanically
failed open).
The following is a description of the APU, MAINT, LOW OIL
PRESSURE, FAULT and OVERSPEED warning lights located on
the flight deck overhead panel.
Hour Meter, Start counter, Resistive Temperature Device
(Event Monitoring Unit)
Faults internal to FADEC
* Low oil quantity
75% Starter Brush Wear
Starter Motor Voltage less than 6V dc
* Main Fuel Valve (mechanically failed open)
Fuel Servo Valve (open)
MAINTENANCE LIGHT (BLUE)
LOW OIL PRESSURE LIGHT (AMBER)
The MAINT light illuminates to provide an APU Warning. Only the
items identified with an asterisk (*) will illuminate the MAINT light due
to electrical open or short in the system.
The LOW OIL PRESSURE light illuminates to identify that oil
pressure is low. During start, the warning light remains illuminated
until oil pressure is normal. If oil pressure is not normal after 100%
engine speed has been reached, the APU will continue to run for an
additional ten seconds and then automatically shut down.
Anti-surge Valve
Bleed Servo Valve (open)
Ambient Pressure Sensor
* Number 1 or Number 2 Speed Sensor (engine speed > 5%)
Start Fuel Purge Solenoid Valve
Ambient Temperature Sensor
* Number 1 or Number 2 Thermocouple
Start Fuel Solenoid Valve
De-oiling Solenoid Valve
Exciter
Aircraft Bleed Air Valve
When the oil pressure is normal and the APU is operating at 100%
engine speed, the warning light will be out. In the event a loss of oil
pressure occurs, the APU will continue to run for ten seconds,
illuminate the warning light, and then automatically shut down.
SPS CT/MAY 1999
Page 13.8
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SUNDSTRAND AEROSPACE
FLIGHT DECK INDICATORS (Continued)
Electrical fault (open/short) in:
FAULT LIGHT (AMBER)
The FAULT light illuminates to identify an automatic shutdown of the
APU. Any of the following conditions will illuminate this indicator:
Fire signal, inlet door not open, battery switch OFF
Rise in EGT less than ∆50°F (∆10°C), six seconds after 5%
speed
High oil temperature
APU maximum EGT exceeded
Input voltage to FADEC is less than 10.5V dc
APU less than 5% speed fifteen seconds after start
command or light off
APU speed greater than 10% at start command
APU speed has decreased to 97% from 100% speed
APU acceleration less than .125% per second for 10
seconds during start or deceleration for 3 seconds
SPS CT/MAY 1999
Main fuel solenoid valve (short only)
Low oil pressure switch (short only)
Number 1 and number 2 speed sensors (engine speed
> 5%)
Number 1 and number 2 thermocouples
Fault internal to FADEC
OVERSPEED LIGHT (AMBER)
The OVERSPEED light illuminates to identify that the APU speed is
greater than or equal to 105% causing the FADEC to initiate an
automatic shutdown. This light can also indicate that the APU start
was not initiated because of faulty speed circuits within the FADEC.
In this case the FADEC will display ECU instead of OVSP.
Figure 13-2. APU Warning and Indicators
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Page 13.9
SUNDSTRAND AEROSPACE
APS 2000
AUXILIARY POWER UNIT
SECTION 14
TROUBLESHOOTING
SPS CT/MAY 1999
Page 14.0
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SUNDSTRAND AEROSPACE
TROUBLESHOOTING
GENERAL
The Troubleshooting System is designed to provide additional
information to aid in the maintenance and repair of the Auxiliary
Power Unit (APU) by downloading the FADEC.
The FADEC stores maintenance information in nonvolatile memory.
This information can be retrieved and analyzed by downloading into
a laptop computer. The computer displays information and
recommended actions from the following stored data:
CONDITIONING MONITORING DATA - This data consists of engine
parameters taken at start and shutdown. Data is provided for each
run of the last twelve APU run cycles
FAULT DATA- This data consists of maintenance and fault
messages for each run of the last twelve APU run cycles.
REQUIRED HARDWARE
To be able to download the FADEC, the following equipment will be
required;
Laptop Computer with at least 3MB of free hard disc space,
a modem, a serial (RS232) connector and a Windows 95
operating system.
FADEC/Computer Interface Cable. (Sundstrand P/N
AGE70013 or TM 90354)
SPS CT/MAY 1999
Page 14.1
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Figure 14-1. Required Hardware
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Page 14.2
SUNDSTRAND AEROSPACE
TROUBLE SHOOTING (Continued)
FADEC DOWNLOAD INSTRUCTIONS
POWER-UP THE COMPUTER - The FADEC Troubleshooting Aid
(FTA) program should automatically launch and the "FTA Overview"
window will appear. Move the cursor over the “Download/
Diagnostics" topic to display instructions.(See Example 14-1)
CLOSE BUTTON - After reviewing the "Download/Diagnostics"
instructions then click on the "Close" Button to remove the "FTA
Overview" window from the screen. (See Example 14-1)
DIAGNOSE BUTTON - Click on the "Diagnose" Button located on
the toolbar, the "Setup" window will appear prompting the operator
for information. (See Example 14-2)
Additional fault information, such as Service Bulletins that address a
fault, will appear in the "Notes" box under SUMMARY. (See Example
14-4)
If multiple faults occur in the same run cycle, multiple tabs will be
displayed. Select the tab of interest by clicking on the tab.
When viewing has been completed, click on the "X" box in the top
right corner of the screen.
Note: Refer to the SUNDSTRAND SERVICE INFORMATION
LETTER (SIL T-47C1-71) for more detailed information.
CONTINUE BUTTON - Fill in the "Setup" information and then Click
on the "Continue" Button. (See Example 14-2) The data will be
automatically downloaded and stored in a file, on disc, with the
results of the diagnoses displayed on the screen. (See Example 143)
The data for each of the last twelve run cycles can be displayed on
the "Fault Information" screen. The data for each run cycle is
available by clicking on the arrows of the RECORD scroll bar. (See
Example 14-3)
All Warnings and Shutdown Faults codes for each run cycle are
displayed in a tab format along with APU, FADEC, AIRCRAFT and
DOWNLOAD information. If an automatic shutdown fault occurs after
start, the ENGINE PARAMETERS will also be displayed. (See
Example 14-3)
Each tab that displays a fault code will provide additional fault
information in the "Fault Description” and "Recommended Action"
boxes under SUMMARY. (See Example 14-3)
SPS CT/MAY 1999
Page 14.3
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SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Example 14-1
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Page 14.4
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Example 14-2
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Page 14.5
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Example 14-3
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Page 14.6
SUNDSTRAND AEROSPACE
SPS CT/MAY 1999
Example 14-4
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restriction on the title page of this document.
Page 14.7