APU

Question 1

Model type of APU?

Answer 1

T – 6 2T – 40 C7B

Question 2

Is the APU certified for ground and air operation?

Answer 2

Only ground operation

Question 3

Location of the APU?

Answer 3

Right hand side aft of the rear pressure dome

Question 4

What is the APU able to supply to the aircraft?

Answer 4

Bleed air and 28 V DC power

Question 5

What provides control for the automatic starting sequence general operation and shutdown of APU?

Answer 5

The electronic sequence unit (ESU)

Question 6

What indications do you get On the ESU if there’s a fault?

Answer 6

Four doll eye magnetic indicators

Question 7

During APU start the starter/generator is powered by what DC system?

Answer 7

The right main bus

Question 8

The APU can be started using what?

Answer 8

Aircraft batteries, external power, or the engine generators

Question 9

The APU fuel system is supplied fuel from where?

Answer 9

I left collecter bay, sent to the FCU fuel control unit on the accessory gearbox which incorporates a mechanically driven fuel pump.

Question 10

What does the fuel control unit automatically schedule?

Answer 10

Fuel for APU starting, acceleration and speed regulation

Question 11

Where is the APU fuel shut off valve located and when is it opened?

Answer 11

Mounted on the rear spar and is automatically opened when the APU PWR switch light is pressed

Question 12

Upon detection of a fire which valve closes?

Answer 12

The APU FUEL SHUTOFF VALVE

Question 13

Where does the APU get its oil for lubrication?

Answer 13

The reduction gearbox housing contains the main components of the APU lubrication system a drive for the oil pump and the oil sump for the system

Question 14

Is the APU intake forward or aft of the exhaust?

Answer 14

Forward

Question 15

The APU fire protection continuously monitors the APU when which bus is powered?

Answer 15

Right essential bus

Question 16

Where is the starter generator mounted on the APU?

Answer 16

On the APU reduction gearbox

Question 17

The APU starter generator system consists of what?

Answer 17

The starter generator, the generator control unit and a bus contactor

Question 18

The bus contactor connects to which bus?

Answer 18

The right main bus

Question 19

What can the APU power?

Answer 19

Can be used to supply all DC and A/C fixed frequency 400 Hz services, charge the main and auxillary batteries and can be used to assist in the aircraft engines starts.

Question 20

The APU is started by the starter generator driving what?

Answer 20

The gas generator through the APU reduction gearbox

Question 21

The GCU and bus contactor are located where?

Answer 21

In the aircraft nose section

Question 22

What indication do you get when the starter is engaged?

Answer 22

The amber starter segment of the start switch light is illuminated

Question 23

At what percentage of rpm does the starter disengage?

Answer 23

70%

Question 24

Once the APU reaches 90% rpm how long does the ESU wait until giving a green run light?

Answer 24

10 seconds

Question 25

What are the starter cranking limits?

Answer 25

One minute on, two minutes off, one minute on, two minutes off, one minute on, 30 minutes off

Question 26

What closes all the necessary bus ties to connect all the DC buses to the APU supply?

Answer 26

DC bus tie logic

Question 27

How is the APU generator cooled?

Answer 27

Buy an integral cooling fan which draws air from a separate inlet duct mounted in the rear fuselage skin.

Question 28

What illuminates to indicate the generator is not supplying the DC system while the APU is running?

Answer 28

A warning segment illuminates On the APU Control Panel, you get an APU caution light on the caution advisory panel and you get A flashing master caution light.

Question 29

What happens to the APU if the external ground power is applied?

Answer 29

The APU GCU automatically removes the APU generator output at the bus contactor if external DC power is applied

Question 30

What happens if the APU generator overheats?

Answer 30

You get a generator over temperature indication on the APU Control Panel and the APU is automatically shut down

Question 31

How do we do APU generator load monitoring?

Answer 31

Select GEN 2 on the DC system, and press the DC load meter on the APU Control Panel

Question 32

Max generator load APU?

Answer 32

300 A displayed as 1.0

Question 33

What illuminates if you have a overspeed condition?

Answer 33

The failure segment on the APU Control Panel, APU caution light and the caution press the reset master switch

Question 34

How is the APU shut down on the last flight on each day?

Answer 34

Using the overspeed test function

Question 35

Which part of the APU supplies the bleed air?

Answer 35

Directly from the APU compressor

Question 36

What does the bleed air switch light do on the APU Control Panel?

Answer 36

The switch opens and closes the bleed air valve in the APU supply line

Question 37

How long should the APU run prior to selecting bleed air on?

Answer 37

20 seconds prior to selecting bleed air on conversely, Bleed air should be selected off 20 seconds prior to shutting down the APU.

Question 38

APU fire detection ?

Answer 38

Uses heat sensing loops and a detector responder

Question 39

When a fire or overheat condition is sensed what do you see?

Answer 39

A red fire warning light on the APU fire protection panel, check fire detection on the warning panel, APU caution light and associated master warning And caution press to reset switch lights, Amber fire bottle lights also illuminate

Question 40

How long does it take before an automatic APU shut down before the fire bottle is emptied to put out the fire?

Answer 40

15 seconds

Question 41

If the APU extinguisher fails to discharge automatically what must you do?

Answer 41

The amber bottle light on the fire protection panel will remain illuminated the fire extinguisher bottle must then be discharged manually using the red guarded extinguisher switch

Question 42

The red guarded extinguisher switch is powered from where?

Answer 42

28 V DC battery bus

Question 43

If you get a fault light on the APU fire protection panel what could this be?

Answer 43

Extinguisher bottle pressure is below a preset value or if a fault develops in the detection loop

Question 44

What does the red indicator disk mean ?

Answer 44

Thermal discharge due to high temperature

Question 45

What does the yellow discharge indicator disk mean?

Answer 45

System activation and the APU fire bottle is empty

Question 46

What prevents a heat induced pressure buildup in the fuel line to the APU When the valve is closed

Answer 46

Incorporates a check valve

Question 47

What annunciations do you get on an APU fire test?

Answer 47

Fuel valve closed amber bottle light, amber fault light, red fire light, check fire detection warning and associated master warning press the reset switch light APU caution light and associated caution press the reset switch light

Question 48

How is the APU compartment cooled?

Answer 48

Uses a fully automatic blower system and APU oil system cooling

Question 49

When is the APU compartment cooling activated?

Answer 49

Whenever the APU power switch light is pressed on the APU Control Panel

Question 50

If the rear Bay exceeds 121°C what will eliminate?

Answer 50

Rear bay overtemp amber light on the APU Control Panel

Question 51

If you get a rear Bay overtemperature does the APU bleed air get cut off?

Answer 51

Yes it Automatically closes the bleed air valve

Question 52

What are the APU limitations?

Answer 52

Approved for ground operations only, ambient temperature limitations of -43°C and positive 48.9°C or ISA +35°C which ever is lower, aircraft must be attended by either a pilot or engineer while the APU is running, operation is prohibited during gravity refuelling, APU bleed air must be selected off prior to engine bleed air been selected on, APU must be shut down prior to takeoff, during ground De-icing APU operation should be avoided. If operation is necessary then bleed air off.

Question 53

Continuous operation of the APU during refuelling is allowed provided that what?

Answer 53

Starting or shutting down the APU is prohibited, left main fuel tank must contain sufficient fuel to ensure continuous operation of the APU, fuel truck must be parked at least 9.2 m away, in case of fuel spillage fuelling be stopped immediately, airports not accustomed to refuelling refueller must be advised that the APU will be running.