Dornier 328Jet - Auxiliary Power UnitThe auxiliary power unit is a gas turbine engine which provides compressed air (bleed air) and ... the bleed port. Some of the air goes to the

READY

APU Control Panel

APU START BUTTONWhen pushed the APU automatic start sequenceis initiated provided APU MASTER button is ON.START (white)– Illuminates until APU RPM of 50% is reached.READY (green)– Illuminates when the APU RPM reaches 94.5%.

APU MASTER BUTTONPushed out (dark) – APU FUEL SOV closed and ECU is de–energized.ON (white)– When pushed in DC power to ECU is provided,

APU FUEL SOV is open, and FUEL SOVCLOSED message on APU page extinguishes.

APU STOP BUTTONWhen pushed a simulated overspeed signal is generatedand the APU automatic shutdown sequence starts.

Dornier 328Jet - Auxiliary Power Unit

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MESSAGE (SYNOPTIC) WARN INHIBITLocation (COLOR)

WARNTONE CONDITION 1 2 3

APU FAIL Automatic shutdown of APU.

CAS Field (AMBER)The following condition may come on with the APU FAIL cautionmessage:

X X

OIL TEMP HIGHAPU Page (AMBER)

Automatic shutdown of APU due to high oil temperature. X X

OIL PRESS LOWAPU Page (AMBER)

Automatic shutdown of APU due to low oil pressure. X X

OVERCURRENT ECUAPU Page (AMBER)

Automatic shutdown of APU due to overcurrent condition. X X

OVERSPEEDAPU Page (AMBER)

Automatic shutdown of APU due to overspeed condition.

OVERTEMP EGTAPU Page (AMBER)

Automatic shutdown of APU due to overtemperature condition. X X

APU LIMIT EXCEED One of the following conditions has occured in flight:CAS Field (AMBER)

X

OIL TEMP HIGHAPU Page (AMBER)

Oil temperature above 1630 C. X

OIL PRESS LOWAPU Page (AMBER)

Oil pressure below 26 PSI. X

OVERCURRENT ECUAPU Page (AMBER)

Overcurrent in an ECU monitored component. X

OVERTEMP EGTAPU Page (AMBER)

EGT above operational limits. X

APU START/STOP

CAS Field (BLUE)Illuminates during APU Start or Shutdown

READY TO LOADAPU Page (BLUE)

APU is ready to accept electrical and/or bleed air loads.

FUEL SOV CLOSEDAPU Page (BLUE)

Illuminates if the APU fuel shut off valve is closed.

Message inhibit logic: 1. WOW, Engines off and Electrical Bus Failure refer to section 12–31–17–042. Takeoff phase3. Landing phase

CAS Field and System Message (Sheet 1 of 2)


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APU SPEED(ANALOG / DIGITAL)

Analog readout of 0 to 108 %.Digital readout of 0 to 120 %.0 to 102% shown in white.

APU Page (WH/AMB/RED)103% to 108% shown in amber.Above 108 % shown in red.

APU EXHAUST GAS TEMP(ANALOG / DIGITAL)

Analog readout of 0 °C to 974 °C during start,0 °C to 732 °C during normal operation.Digital readout of 00 to 999 0CDuring start and normal operation EGT between 0 0C and 680 0Cshown in white.During start (0 to 49% RPM):

APU Page (WH/AMB/RED)

– between 680 0C and 974 0C– above 974 0C shown in red.During start (50 to 87% RPM)– between 680 0C and 732 0C (EGT decreases in relation to RPM increase) shown in amber– above 732 0C – 974 0C (EGT decreases in relation to RPM increase) shown in red.

Digital readout of APU – EGT

NOTE: Automatic shut down features except overspeed are disabled with weight off wheels.That means an APU limit exceedance (overtemp,overspeed,overcurrent ECU, HOT,LOP) on ground leads to an APU S/D. In flight only an overspeed of the APU leads to aS/D of the APU. All other limit exceedances lead to the APU LIMIT EXCEED messageon the CAS field.

CAS Field and System Message (Sheet 2 of 2)


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CAS Field Messages on EICAS Display


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Indications/Messages on APU Page (Sheet 1 of 2)


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Indications/Messages on APU Page (Sheet 2 of 2)


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Messages on SYS MAINT Page


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AUXILIARY POWER UNIT (APU)

GENERALThe auxiliary power unit is a gas turbine engine which provides compressed air (bleed air) andelectrical power on ground or in–flight (refer to Section 2 – LIMITATIONS in the AFM).

Except for the airplane batteries and fuel supply, the APU is independent of other airplanesystems. It is mounted in the fuselage tail cone.

An APU control panel, located on the overhead panel in the flight compartment, contains anAPU MASTER button, an APU STOP button, and an APU START button.

The APU has an independent fuel feed system (refer to Section 12–28–00–00 – FUEL).

The APU comprises the following four major components:

– the power section– the air inlet– the gearbox assembly– the controls and the accessories.

APU POWER SECTIONThe power section is a single shaft gas–turbine using a single–stage centrifugal compressor, areverse flow annular combustion chamber and a single–stage radial turbine.

CompressorThe compressor provides compressed air for combustion and bleed air for the airplane ECS. Airenters the inlet, is compressed in a centrifugal impeller and then discharged through a diffuserand de–swirl deflector into the combustion chamber.

Combustion ChamberThe combustion chamber is located within the turbine housing. The turbine housing provides aflow path boundary for the compressed air and delivers the air to the combustion chamber andthe bleed port. Some of the air goes to the ejector system, via the combustion drain fitting,where it is used to vent the gearbox. The compressed air passes through holes in thecombustion chamber where fuel is added and burned. The air is then discharged into theturbine section.

Turbine SectionThe turbine section consists of a single–stage, fixed area radial inflow turbine and a stator. Therotor is mounted on a common shaft with the compressor rotor. Hot gases coming from thecombustion chamber flow into the turbine that drives the compressor and gear box. Afterpassing through a turbine wheel, the gases discharge axially through a short diffusing section.


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APU AIR INLET SECTIONThe functions of the air inlet section are to provide sufficient air for the APU engine, to preventforeign objects entering the compressor by means of an inlet screen, and to provide thestructural connection of the power section to the gear box.

APU GEAR BOX ASSEMBLYThe gear box assembly is mounted on the air inlet section to provide the necessary reduction ofAPU engine speed and to drive the accessories and the APU starter generator.

In addition to the mounting pad for the starter/genarator the gear box has the mounting pads forthe oil pump (the oil pump provides the mounting pad for the fuel control unit) and the mountingframe. It also has bosses for:

– the oil filter,– the Low Oil Pressure (LOP) switch,– the High Oil Temperature (HOT) switch,– the monopole speed sensor,– the gearbox vent,– the oil drain plug,– the oil fill cap.

APU Oil SystemThe APU has a self–contained closed lubrication system. The system is totally integrated withinthe accessory gear box and provides required oil cooling without the need for an external heatexchanger. Oil cooling is accomplished by fins extending into the air inlet casing.

The oil sump is is an integral part of the gear box and provides a capacity of 2 quarts with ausable capacity of 0.5 quarts. The possibility of safe drainage of the entire oil system isaccomplished through the oil drain plug with an integral magnetic plug which is located at thebottom of the gear case.

The gear case vent is provided with an ejector which is driven by compressor bleed air takenfrom the combustion drain fitting. The discharge flow from the ejector (gear case vent andcombustion drain fitting) is then routed to the exhaust housing of the APU where it is mixed withthe exhaust gas of the APU and discharged overboard.

ExhaustThe exhaust is directed upwards to prevent re–ingestion of exhaust gas and protection ofground crew.The exhaust duct has an ejector at each end, which helps to provide APU compartmentventilation and cooling of the starter/generator. The front ejector is formed where the nozzle ofthe APU goes into the exhaust duct. The rear ejector is formed by the rear of the exhaust ductand the opening in the tail cone. When the exhaust gas flows through the exhaust duct:

– at the front ejector, the air in the APU compartment is drawn into the gas flow. This creates aflow of air through the APU compartment.

– at the rear ejector, the gas flow draws the air from the exhaust shroud, which in turn aids thestarter/generator cooling.


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APU FUEL AND CONTROL SYSTEMThe APU fuel and control system provides filtered, metered and atomized fuel for start,acceleration and governed speed control of the APU. The system is fully automatic andreceives its fuel from the APU fuel feed system.

The APU fuel system is supplied with fuel from the feeder tanks in each wing. The feeder tanksmust have a minimum of 78 kg (170lbs) in each tank for continued APU operation, otherwisethe APU can be starved of fuel causing RPM fluctuation and/or APU shutdown (refer to Section12–28–00–00 for more details of the APU fuel feed system).

The controlling system consists of the Fuel Control Unit (FCU) which produces and regulatesthe high pressure fuel flow during engine acceleration and normal operation. It also increases ordecreases the fuel flow as necessary to accommodate changes in engine load and thus keepsthe speed of the APU constant. The FCU is attached to the oil pump which is located at thefront of the APU engine and is electrically controlled by the Electronic Control Unit (ECU) that islocated on the RH side of the tail cone. Together the FCU and ECU control the fuel scheduling,speed control, valve sequencing and automatic shutdown.

APU Fuel DistributionThe distribution system is supplied with metered fuel from the FCU. When the APU is started,the fuel solenoid valve is activated to open at 10% APU RPM and fuel is permitted to flow to thefuel flow divider valve. The valve routes the fuel to the fuel manifolds and to the primary andsecondary fuel nozzles which inject the atomized fuel into the combustion chamber.

FUEL SOLENOID VALVEThe fuel solenoid valve is located between the FCU and the manifolds and fuel nozzles. Thevalve is normally closed. During the APU starting phase at 10�percent RPM, the ECU causesthe fuel solenoid valve to open to permit fuel flow. During APU shutdown regardless of whethernormal, automatic or emergency APU shut down is initiated, electrical power is removed toclose the fuel solenoid valve.

FUEL FLOW DIVIDER VALVEThe fuel flow divider valve is located between the fuel solenoid valve and the fuel manifolds.When the fuel solenoid valve is open, fuel is routed to the inlet port of the valve. During thestarting and initial acceleration phase of the engine, the valve only permits fuel flow to theprimary fuel manifold and primary fuel nozzles. As the APU engine speed and the fuel pressureincreases the valve automatically opens to permit additional fuel flow to the secondary manifoldand nozzles. The flow divider valve is preset and is not adjustable.

FUEL MANIFOLDS AND FUEL NOZZLESThe primary and secondary fuel manifolds are connected between the fuel nozzles and fuel flowdivider. The primary fuel manifold supplies fuel to nozzles at the 2, 7 and 11 o’clock positionsand the secondary fuel manifold supplies fuel to nozzles at the 1, 5 and 9 o’clock positions.Three primary and three secondary fuel nozzles are installed in the turbine housing. The fuelnozzles supply atomized fuel to the combution chamber to achieve optimum combustion duringoperation.


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COMBUSTION DRAIN FITTINGThe combustion drain is installed at the lowest point in the turbine housing. It permits theoverboard draining of fuel which can accumulate following an aborted start. The orifice of thedrain fitting is open at all times and provides the bleed air for the ejector system to vent the APUgearbox.

Fuel Control Unit (FCU)When APU start is initiated, fuel from the feed line enters the FCU through the fuel inlet port andpasses through a low pressure inlet filter.

A high pressure pump simultaneously rotates when the APU engine is started. As the highpressure pump starts to rotate, the fuel pressure increases until operating pressure is attained.From the output side of the high pressure pump, pressurized fuel is internally routed to themetering valve, the differential pressure valve and the ultimate pressure relief valve.

During the engine start phase and until engine speed reaches 10 percent, the fuel solenoidvalve remains closed. The fuel pressure generated by the high pressure pump is automaticallyrouted to the differential pressure valve which opens to return all the unwanted fuel pressure tothe inlet side of the fuel pump and bypass the metering valve.

At 10 percent APU speed, the ECU energizes the fuel solenoid valve to open and fuel ispermitted to flow to the APU combustion chamber. At the same time, the differential pressurevalve maintains a constant pressure drop across the metering valve by bypassing fuel back tothe inlet side of the fuel pump. The valve flow area is modulated by the torque motor whichreceives variable input signals from the ECU. The correct fuel flow for APU demand, whetheraccelerating, unloaded or with bleed air and generator loads applied is controlled automaticallyby the ECU speed sensor the EGT thermocouple and fuel control circuits. The ECU transmitssignals to the torque motor which regulates the fuel flow through the metering valve to meetAPU demands.

During APU shutdown or when excess pressure occurs, the ultimate relief valve opens tobypass the pressure back to the inlet side of the high pressure pump.

Engine Control Unit (ECU)The ECU of the APU provides completely automatic operation of the APU for all ambientconditions and operational modes.

The ECU provides for shaft power priority. In the event that the applied load exceeds the APUcapabilities, the pneumatic load is adjusted by closing the load control valve to maintain theoperating parameters within their normal limits.


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The ECU is mounted in front of the APU fire wall and monitors switch point actuation andde–actuation during starting, governed speed operation (normal operation), and shut down. TheECU also senses APU engine overspeed, exhaust gas temperature, oil pressure, oiltemperature, and overcurrent conditions during APU operation. Should any fault of themonitored parameters be sensed by the ECU, the APU will be shut down immediately with theairplane on the ground (WOW). If the airplane is in flight, only the overspeed condition willcause an APU shutdown. Signals from sensors on the APU are relayed through the ECU to theElectronic Indicating, Caution and Advisory System (EICAS), the ECS page, the ELECTRICpage, the FUEL page, the APU page, and the APU control panel.

BUILT–IN TESTThe ECU is equipped with a built–in test (BITE) circuit to provide fault shut down indicators.There are three BITE indicators, located on the face of the controller above the electricalconnectors, for visual identification of unscheduled shut down faults. The indicators are binarycoded, magnetic latching devices. The fault latches can only be reset by cycling the APUMASTER button off and on. The decoded BITE information is listed below:

BITE Number Decoded BITE Information

1 2 3

� � � Reset Condition

� � � Overspeed

� � � Overtemperature

� � � Low Oil Pressure

� � � Overcurrent to ECU

� � � Loss of EGT Thermocouple Signal

� � � Loss of Speed Signal

� � � High Oil Temperature

AUTOMATIC START SEQUENCESet the MFD 1 or MFD 2 to the FUEL Page, do a check of the fuel level in each feeder tank.

– If the fuel level in either tank is at or near to 78 kg (170lbs) set the electrical booster pumpsto ON.

NOTE: The feeder tanks in each wing must be maintained at 78 kg (170lbs) to operate the APUsatisfactory. If the fuel level in either feeder tank drops below 78 kg (170lbs), it cancause RPM fluctuation and/or APU shutdown:

– If the APU is to be used for an extended period, set the electrical booster pumps to ON,

– set the MFD 1 or MFD 2 to the APU Page.


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With the APU MASTER button set to ON, momentarily push the APU START button:

– DC electrical power is provided to the APU starter/generator. The APU engine starts to rotateand a speed signal is transmitted from the monopole speed pickup to the ECU.

– At 10% APU RPM the ECU provides power to the ignition unit and opens the FCU fuelshut–off valve and ignition occurs. The APU engine accelerates controlled by the ECU whichmonitors the EGT during the start to minimize the turbine stress level.The APU start should be aborted if there is no visible increase in EGT and the RPMstagnates around 30 percent.

NOTE: Further starts are allowed after APU roll down.

– At 50% APU RPM electrical power is removed from the APU starter/generator, the STARTcaption in the APU START button goes out and the APU accelerates on its own.

– At 94.5% APU RPM after a time delay of between 3 and 5 seconds the ignition unit isde–energized. The APU can now provide bleed air and/or DC power, as required. The greenREADY light in the START button on the APU control panel as well as the blue READY TOLOAD message on the APU page will be illuminated.

AUTOMATIC SHUTDOWN SEQUENCEThe ECU automatically shuts down the APU engine if one of the following faults occur withWOW:

– Low oil pressure: Armed above 94.5% APU RPM after a 10 seconds time delay.

– High EGT: During start:up to 49% RPM: 974°CBetween 50 and 87% RPM: 732 °C – 974 °CAbove 87% RPM: 732 °CDuring normal operating (governed speed): 732 °C

– Overspeed: At 110% APU RPM with a backup at 109% speed.

– Overcurrent to ECU: If a short circuit occurs in an ECU driven component, the ECUrecognizes the overcurrent after a three second time delay.

– Loss of speed signal: The ECU recognizes a zero speed signal.

– Loss of EGT signal: The ECU senses an open circuit.

– High oil temperature: At 163 °C after a one second time delay.

The ECU will automatically shut down the APU in flight only if the following fault occurs:

– Overspeed (this provides best availability of the APU for essential conditions).


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The EICAS shows the amber APU FAIL message on the EICAS primary page (CAS field) andthe reason for the shutdown on the APU page and the SYS MAINT page. The fault shutdownreason is latched within the ECU until the APU MASTER button is cycled Off and ON again. Inaddition to these indications the ECU itself provides an auto shutdown indication (BITEindicators).

NORMAL SHUTDOWN SEQUENCEThe APU engine can be shutdown at the existing load condition by pressing the APU STOPbutton on the APU control panel which inserts a false overspeed signal into the speed sensingcircuit, causing the APU to shut down. During APU shutdown the APU overspeed warning issuppresed.

CAUTION: AVOID CYCLING MASTER POWER DURING APU ROLL DOWN. THE EFFECTSOF CYCLING THE MASTER POWER ABOVE 10 PERCENT RPM WILL CAUSE APREMATURE ECU RESET, THUS GENERATING A LOW ENERGY RESTART,THE RESULT BEING A HIGH EGT INDICATION AND TORCHING FROM THEAPU TAILPIPE. A RESTART IS ALLOWED WITHIN THE RESTART ENVELOPE AFTER ACOMPLETE ROLL DOWN OF THE APU. THIS IS ALSO VALID AFTER ANAUTOMATIC SHUTDOWN OF THE APU. WAIT TWO MINUTES AFTER APU MASTER SHUTDOWN BEFORE RESTART(MASTER BUTTON ON).

ABNORMAL SHUTDOWN SEQUENCEThe APU engine must be manually shutdown if engine limitations or parameters are exceededor if abnormal noises are audible (refer to paragraph Normal Shutdown Sequence this Section).If a limit has benn exceeded, the EICAS displays the amber APU LIMIT EXCEED message onthe EICAS primary page (CAS field). Also the limit that has been exceeded, is displayed on theAPU page and the SYS MAINT page. The fault reason is latched in the ECU until the APUMASTER button is cycled OFF and ON again.

EMERGENCY SHUTDOWN SEQUENCEThe APU must be stopped if a fire condition occurs. This is done from the APU FIRE buttoneither, the overhead panel in the flight compartment, or from the OUTBOARD panel on the LHside of the forward fuselage. The FIRE button on the overhead panel can be used in flight or onthe ground, the FIRE button on the OUTBOARD panel can only be used on the ground.Pushing either of these buttons opens switches in the APU control circuit, which initiates theAPU shutdown. (refer to Section 12–26–00–00 – FIRE PROTECTION).

WARNING: NEVER TRY TO RESTART AN APU AFTER ACTUAL FIRE.


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APU BLEED AIR SYSTEMThe APU bleed air system consists of the load control valve (LCV) and the stainless steel bleedair ducting that is connected to the APU engine compressor section. The LCV is installed in thetail cone on the LH side. Two APU duct check valves (forward and rear) are located upstream ofthe LCV. The forward check valve prevents reverse flow of bleed air from the main engines tothe HP ground air connections and to the LCV. The rear check valve prevents reverse flow of airfrom the ground connections through the LCV.

During the APU engine start and acceleration phase, the electrical circuit remains de–energizedand the LCV closed. When the APU RPM is 94.5 percent or above, after a time delay ofbetween 3 and 5 seconds the ECU completes the electrical circuit. The READY light in theSTART button on the APU control panel comes on.

NOTE: Wait two minutes before selecting APU bleed air after APU has stabilized.

When the APU BLEED button is pressed, the LCV is energized to the open position, the ONlight comes on and bleed air flow from the APU engine compressor section is permitted to theaircraft bleed system.When the APU BLEED button is pressed out, the LCV closes and the ON light goes out.Alternatively when the APU STOP button is pressed or the APU MASTER button is pressed out,this will also cause the LCV to close followed by APU shutdown.

INDICATIONSSystem operating status is indicated by lights in the APU control panel buttons and by thefollowing messages and synoptic (refer to Subsection 12–49–01–00):

On primary EICAS page only:– APU FAIL caution message (amber)– APU LIMIT EXCEED caution message (amber)– APU START/STOP status message (blue)

On APU page only:– OIL TEMP HIGH caution message (amber)– OIL PRESS LOW caution message (amber)– OVERCURRENT ECU caution message (amber)– OVERSPEED caution message (amber)– OVER TEMP EGT caution message (amber)– READY TO LOAD status message (blue)– FUEL SOV CLOSED status message (blue)– APU speed synoptic– APU EGT synoptic.

On SYS MAINT page only:– OIL TEMP HIGH caution message (amber)– OIL PRESS LOW caution message (amber)– OVERCURRENT ECU caution message (amber)– OVERSPEED caution message (amber)– OVERTEMP EGT caution message (amber)


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Documents

Dornier 328Jet - Auxiliary Power UnitThe auxiliary power unit is a gas turbine engine which provides compressed air (bleed air) and ... the bleed port. Some of the air goes to the