Q400 Pneumatics 1

12.19.1 Introduction

The Auxiliary Power Unit (APU) replaces the standard composite tailcone with a titanium tailconeand firewall. The APU is accessed by two clamshell type doors on the bottom of the tail cone. Itconsists of a gas turbine engine driving a DC starter-generator. The APU supplies bleed air forthe Environmental Control System (ECS), and 28 VDC to the electrical system. The APU cannotbe operated in flight.

12.19.2 General

The start control, normal operation, and malfunction monitoring of the APU is automatically per-formed by the APU FADEC. The APU starter-generator can be powered from either theaeroplane main battery or external power. Intake air is drawn through a screened inlet duct onthe right rear of the fuselage. Exhaust gases flow through an exhaust ejector and are dischargedthrough an upwards pointing outlet at the aft end of the titanium tailcone. The APU is protectedby its own automatic fire detection and extinguishing system that continuously monitors the APUand its compartment whenever electrical power is supplied to the system. The APU control panelis mounted on the overhead console in the flight deck.APU Louvered Inlet Cover

A louvered cover is provided for the APU Air Inlet to help prevent snow and sleet from enteringthe APU Inlet when the aeroplane is on a long turnaround or remaining overnight.

Dash8 - Q400 - Pneumatics

Page 1

12.19.3 Controls and Indications - Auxiliary Power Unit


Page 2

Figure 12.19-1 APU Control Panel

APU CONTROL

START GEN BL AIR

ON

WARN

OPEN

GEN OHT

PWR

RUN

FAIL

STARTER

4 1 5 2 3


Page 3

APU CONTROL PANEL CALLOUTS

1. PWR SWITCHLIGHT (alternate action)

PUSH - arms APU start circuits and opens the APU fuel valve, APU FUEL VALVE OPENlight (green) shown on the APU fire protection panel- only arms if aeroplane on ground, no fire detected, and EXTG switch not selectedRUN segment (green)- APU is at operating speed after the START switchlight is pushedPUSH - RUN segment (out)- closes APU fuel valve, APU FUEL VALVE CLOSED light (white) shown on the APU fire

protection panel, and the APU stopsFAIL - a failure is detected and the APU automatically stops

2. START SWITCHLIGHT (alternate action)

PUSH - STARTER segment (amber)- starts automatic APU start sequenceSTARTER segment (out)- APU start sequence complete or stopped

3. GEN SWITCHLIGHT (alternate action)

PUSH - ON segment (green)- APU starter-generator is supplying DC powerPUSH - ON segment (out)- selects APU generator off lineWARN segment (amber)- APU starter-generator off line with APU running

4. BL AIR SWITCHLIGHT (alternate action)

PUSH - OPEN segment (green)- APU bleed air valve open- APU bleed air supplies air to the ECS if engine bleed air is offPUSH - OPEN segment (out)- APU bleed air valve is closed- selects APU bleed air off

5. GEN OHT ADVISORY LIGHT

GEN OHT segment (amber)APU starter-generator overheat conditionAPU automatically shuts down


Page 4

Figure 12.19-2 APU Fire Protection Panel (1 of 2)

OP

EN

CL

OS

ED

AP

U

FU

EL

VA

LV

EB

TL

AR

M

EX

TG

FIR

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FIR

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BT

L L

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FA

UL

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LT

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WD

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UL

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BF

AU

LT

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21 3 4 5

7

6


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APU FIRE PROTECTION PANEL CALLOUTS

1. FUEL SHUT-OFF VALVE CLOSED ADVISORY LIGHT (white)- APU fuel shut-off valve closed- APU shutdown, manually or automatically

2. FUEL SHUT-OFF VALVE OPEN ADVISORY LIGHT (green)- APU fuel shut-off valve open- PWR switchlight pushed- APU circuits armed for starting or fire test

3. FIRE ADVISORY LIGHT (red)- APU fire detected- after 7 seconds extiguishing agent automatically releases, and amber BTL ARM light

goes out

4. EXTG SWITCHLIGHT (guarded, alternate action)

EXTG segment (white)- APU fire extinguisher bottle can be activated manually if BTL ARM light is onPUSH - EXTG segment (out)- APU fire bottle cannot be activated, or has been set off

5. BOTTLE LOW LIGHT (amber)- fire extinguisher bottle is low or empty

6. FAULT ADVISORY LIGHT (AMBER)- fault in the APU fire extinguisher system- fault in the APU FPP

7. BTL ARM ADVISORY LIGHT(amber)- APU fire extinguisher bottle ready to be activated(OUT)- APU fire extinguishing bottle cannot be activated- no power to the system


Page 6

Figure 12.19-3 APU Fire Protection Panel (2 of 2)

OP

EN

CL

OS

ED

AP

U

FU

EL

VA

LV

EB

TL

AR

M

EX

TG

FIR

E

FIR

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ES

T

BT

L L

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UL

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A

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UL

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B

8


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APU FIRE PROTECTION PANEL CALLOUTS (contd)

8. FIRE TEST PUSHBUTTON (momentary action)

PUSH AND HOLD - check the following lights: MASTER WARNING light (red) flashes CHECK FIRE DET warning light (red) flashes FIRE segment (red) BTL ARM light (amber) FUEL VALVE OPEN (out) FUEL VALVE CLOSED (white) FAULT light (amber) EXTG segment (white)RELEASE - check the FUEL VALVE OPEN (green) comes on


Page 8

Figure 12.19-4 MFD Electrical Page with APU Generator Operating (1 of 2)

FLAPDEG

35

1050

35

3

1

ELECTRICAL AC EXTPOWER

DC EXTPOWER

LOAD1 1 51 1 51 1 5

. 06

. 06

. 06

1 1 51 1 51 1 5

. 06

. 06

. 06

ABC

ABC

+22+22+22

+1. 00- . 34- . 34

+1. 00

+1. 00 +1. 00

APU GEN

DC GENLOAD1 2

TRULOAD1 2

LOADBATT

C

VOLTDC BUS

RL

MAINAUX

STBY

ESSMAINSEC

AC GEN 1

AC GEN 1

VOLT LOAD

VOLT LOAD28.128.128.1

28.128.128.1

SPOILERS

R1R

ELEV

RUDLO L1L

ELEVHYD PRESS PSI HYD QTY %

PK BRK STBY 1 2 3 1 2 33000 0 30003000 0 100 100 100

2 1

+0. 00 . 00


Page 9

MFD ELECTRICAL PAGE CALLOUTS

1. DIGITAL DISPLAY OF APU GENERATOR LOAD (white)

APU GEN (white)LOAD (cyan)- is activated only if the APU is installed depending on the aeroplane configuration- the load demand on the APU generator is displayed in the following format:

+ sign is displayed on the left of the lead digit to indicate an overload of the DCpower source

nothing is displayed when the load is in the expected range

leading zero is suppressed in the lead digit position

digital number gives the rate of the load, with 1.00 equal to 100% of load

- examples: .60 indicates that the DC generator or TRU is loaded at 60% of the maximum out-

put.

+1.30 indicates an overload of the DC generator or TRU

2. BATTERY LOAD AND TEMPERATURE ANNUNCIATION AREA

BATT (white)LOAD, C (cyan)MAIN, AUX, STBY (white)

3. DIGITAL DISPLAY OF BATTERY LOAD (white)- displays the load of the battery- + or - sign on the left of the lead digit, whether the battery is in overcharge (+ displayed)

or in discharge (- displayed)- nothing is displayed when the battery is in charge within the expected range- leading zero is suppressed in the lead digit position- digital number gives the rate of the load, with 1.00 equal to 100% of load- examples:

.60 indicates that the battery is in charge at 60% of its maximum rate of charge

-1.30 indicates that the battery is discharging at 30% over the maximum rate ofdischarge


Page 10

Figure 12.19-5 MFD Electrical Page with APU Generator Operating (2 of 2)

ELECTRICAL

LOAD

AB

C

AB

C

+22+19+20

. 06 . 04 . 03

. 64

. 00 . 00

APU GEN

DC GENLOAD1 2

TRULOAD1 2

LOADBATT

C

VOLTDC BUS

RL

MAIN

AUX

STBY

ESS

MAIN

SEC

AC GEN 1

AC GEN 2

VOLT LOAD

VOLT LOAD

HYD PRESS PSI HYD QTY %PK BRK STBY 1 2 3 1 2 3

3000 0 30003000 0 100 100 100

FLAPDEG

35

1050

SPOILERS

RI

RELEV

RUDLO LI

LELEV

RO

.00 . 00

0 00

. 00

. 00

. 00

000

. 00

. 00

. 00

27.228.028.0

27.228.028.0

45

6


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MFD ELECTRICAL PAGE CALLOUTS (contd)

4. DIGITAL DISPLAY OF BATTERY TEMPERATURE- battery temperature digits are displayed in white with a + or - sign on the left of the lead

digit, when the temperature is within normal limits- when the temperature is in the range (+50C to +65C) the digits turn yellow- when the temperature exceeds 65C the digits are displayed in red

5. DC bus voltage annunciation area

DC BUS (white)L, R (white)VOLT (cyan)

6. DIGITAL DISPLAY OF DC BUS VOLTAGE (white)- indicates the voltage on the associated bus


Page 12

Figure 12.19-6 APU Fuel Schematic

ENGINE FEED LINEAPU FEED

LNE

DRYBAY

INLETSTRAINER

APU SHUT-OFFVALVE

AIRCRAFT

CLENGINE

COLLECTORBAY


Page 13

12.19.4 Auxiliary Power Unit - Description

12.19.4.1 APU Fuel System

APU fuel is supplied from the left wing collector bay through an APU shutoff valve. A rigid fuelline is routed from the shutoff valve to the APU/tailcone firewall (Figure 12.19-6), outside thepressurized part of the fuselage. A gravity-fed, APU-driven fuel pump keeps positive fuel pres-sure to the APU engine.

The APU shutoff valve opens when the APU PWR switchlight is pushed and closes when theAPU is shut down. The position of the shutoff valve is shown on the APU Fire Protection Panel(FPP). Fuel is automatically scheduled for starting, acceleration, and speed regulation.

The APU shutoff valve will close if:

PWR switchlight is pushed off Fire is detected in the tailcone EXTG switchlight is pushed Aeroplane is in flight


Page 14

Figure 12.19-7 Starter-Generator Schematic

GE

N

ST

BY

GC

UG

CU

#1 D

CG

EN

#1 D

CG

EN

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CG

EN

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12.19.4.2 Starter-Generator

The APU has a gearbox mounted 28 VDC starter-generator (Figure 12.19-7). An APU startrequires either aeroplane batteries or external power. When the APU starts, the starter staysengaged until the APU reaches half its operating speed. When the APU is operating, the RUNsegment comes on to show that, the generator mode is available to supply 28 VDC. The WARNsegment of the GEN switchlight comes on when the generator is off-line.

The APU electrical load and voltage can be monitored on the ELECTRICAL page of the MFD.

After the aeroplane main engine DC starter-generators are on line, the APU generator will con-tinue to supply power in parallel to the DC buses. The APU system will automatically preventAPU generator output if external AC or DC power is applied to the aeroplane.

The starter-generator is cooled by air which enters through a metal mask screen at the bottomforward section of the tailcone and exits through the tailcone right side door (Figure 12.19-8). Ifthe starter-generator overheats, the APU will automatically shut down, shown by the GEN HOTadvisory light.

If a starter-generator fault is detected, the:

Starter-generator is removed from the right main feeder bus ON segment of the GEN switchlight goes out WARN segment of the GEN switchlight goes amber

The APU utilizes 2x40 Ahr NiCad batteries for starting when external DC power is not available.The characteristics of the Starter are such that the initial current draw is not highly dependent onthe load being driven, but more a function of the Starter itself, and the state of charge of the bat-teries.Due to the high inrush currents during starting, there is a drop in voltage at the battery, andhence the Main Buses. Technical data shows that for a battery only start, with a battery at100% charge, bus voltage drops to about 20 VDC (value varies with temperature). For a batteryat 50% charge, the bus voltage drops to about 18 VDC (value varies with temperature). It is clearthat starting the APU using batteries with insufficient charge can lead to system problems whichjeopardize successful start.


Page 16

Figure 12.19-8 APU Starter-Generator Air Inlet and Exhaust

7. Starter/Generator Exhaust Air Duct Opening. 8. Starter/Generator Exhaust Air Duct. 9. APU Ventilation Inlet.10. APU Starter/Generator Air Inlet.

LEGEND

1. Drain Mast.2. Drain Outlet Opening.3. Left APU Door.4. Strut Push-Release.5. Telescopic Struts.6. Right APU Door.

5

9

1

23

4

10

5

4

6

7

8


Page 17

12.19.4.3 APU Compartment Ventilation

APU compartment ventilation is established by the APU exhaust air ejector system.

Ventilation air enters the compartment through a screened inlet near the bottom forward end ofthe tailcone. Air is directed by a composite duct to the area in front of the oil sump to assist oilcooling. Air then flows around the APU before being mixed with the exhaust ejector flow.


Page 18

Figure 12.19-9 APU Bleed Air System Schematic

AP

U B

LE

ED

MA

NIF

OLD

FIR

EW

ALL

AP

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CK

VA

LV

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PU

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ON

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#1


Page 19

12.19.5 APU Bleed-Air System

When the APU is operating, the APU bleed air valve can be opened by pushing the BL AIRswitchlight on the APU control panel. APU bleed air supplies bleed air for the ECS, and holds theCabin Pressure Control System (CPCS) aft safety valve open (Figure 12.19-9). When the valveis not closed, the OPEN segment (green) of the BL AIR switchlight will come on. The bleed airsupply is reduced if the APU exhaust temperature reaches an established temperature limit. Thisgives APU generator load priority over bleed air.

An APU check valve and wing duct check valves prevent APU bleed air from entering the enginebleed air supply, including airframe de-icing. If either main engine BLEED air toggle switch is setto 1 or 2, the APU BL AIR switchlight is automatically de-energized. This ensures that bleed air isnot supplied from the engines and APU at the same time.


Page 20

Figure 12.19-10 APU Fire Detection Schematic

CONTROLAMPLIFIER

APUAPD

SENSOR

APUFIREBTL

SQUIB

PRESSURESWITCH

FIREPROTECTION

PANEL

MASTERWARNING/

CAUTION PANEL


Page 21

12.19.6 APU Fire Protection

The APU has a fully automatic fire detection and extinguishing system (Figure 12.19-10). Thesystem monitors the APU hot section and exhaust whenever the right essential 28 VDC bus isenergized. The system is operated from the Fire Protection Panel (FPP) on the overhead con-sole.

The system includes a:

stainless steel fire extinguisher bottle and distribution tubing loop sensor routed along the tailcone above the APU control circuit

When a fire or overheat condition is sensed by the detection loop, the:

FIRE light (red), on the FPP illuminates MASTER WARNING light flashes (red) CHECK FIRE DET warning light flashes (red) BTL ARM advisory light (amber); then (out) if the bottle has discharged APU FUEL VALVE CLOSED advisory light (white) illuminates APU FUEL VALVE OPEN advisory light (out) extinguishes EXTG segment of EXTG switchlight (white) illuminates MASTER CAUTION light flashes (amber) APU caution light (amber) illuminates

12.19.7 APU Fire Extinguishing

If a fire is detected, the APU automatically shuts down and the fire extinguishing agent isreleased after 7 seconds. If automatic fire extinguisher discharge fails, the BTL ARM light stayson. The guarded EXTG switchlight can be pushed to discharge the fire extinguishing agent, if theBTL ARM is on.

NOTE: Once the bottle has been discharged, restarting the APU is prevented until the bottlehas been replaced.


Page 22

12.19.8 APU Faults

The APU system can detect a fault, isolate the APU and supply protection. The system will pro-tect and shut down the APU.

The APU system monitors:

Overspeed Underspeed Start Failure Accelerate Failure EGT overtemperature Low Oil pressure High Oil temperature Failed Sensors Failed Valves, relays, circuits Internal failure

If an APU fault is detected, the:

APU automatically shuts down FAIL segment of the APU PWR switchlight (amber) APU FUEL VALVE CLOSED advisory light (white) APU FUEL VALVE OPEN advisory light (out) APU caution light (amber)

The APU PWR switchlight must be reselected after an automatic shutdown or failure to start.

12.19.9 APU Shutdown

Before shutting down the APU, close the bleed air valve and select the GEN off. Normal APUshut down is then accomplished by pushing the PWR switchlight.

12.19.10 Limitations

Item 1 (Ref. Para 12.19.4.3)With composite cooling duct removed, ambient temperature limitation applies: 30C or ISA+25C, whichever is lower.

Item 2For APU operation with the Air Inlet Louvre installed, ambient temperature Limitation of 21Capplies.


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Q400 Pneumatics 1