APU

Question 1

The APU supplies bleed air and electrical power.

Answer 1

Electrical power has priority over bleed air.

Question 2

The APU can be started and operated to the airplane maximum operating altitude.

Answer 2

Electrical power is available throughout the airplane operating envelope.

Question 3

With the APU SEL in the OFF position;

Answer 3

the APU bleed air isolation valve is closed, a normal shutdown is initiated and the auto shutdown fault logic is reset.

Question 4

ON is the APU operating position.

Answer 4

Moving the APU SEL to the ON position

opens the APU fuel valve and inlet door,

activates an AC or DC fuel pump and powers the APU controller.

Question 5

START is a momentary position

Answer 5

spring-loaded to return to ON. It initiates the automatic start sequence.

Question 6

The APU FAULT light is illuminated if

Answer 6

an APU fault and / or fire is detected,

if the APU has shutdown due to a fault and / or fire,

or momentarily during the APU controller self-test.

Question 7

The APU is started either by

Answer 7

an electric start motor or an air turbine starter.

Question 8

APU Battery

Main Battery for APU

Answer 8

APU Battery powers Electric Starter

Main Battery

Inlet Door

Fuel Valve

Fire Detection System

Question 9

The air turbine starter uses

Answer 9

bleed duct pressure or ground air.

Question 10

Starter selection is automatic.

The air turbine starter has

Answer 10

priority over the electric start motor when there is sufficient bleed air duct pressure.

Question 11

APU fuel is supplied from

Answer 11

the left fuel manifold by any operating AC fuel pump or the DC fuel pump.

Question 12

With AC power available and the APU SEL in the ON position,

Answer 12

the left forward fuel pump operates automatically.

Question 13

If AC power is not available or no AC pump pressurizes the left fuel manifold

Answer 13

the DC pump in the left main tank provides APU fuel.

Question 14

When the APU air inlet door reaches the full open position

Answer 14

the starter engages.

Question 15

When the APU reaches approximately 50 % RPM

Answer 15

the starter disengages and ignition is turned off.

Question 16

If the start fails,

Answer 16

the APU shuts down automatically.

The EICAS message APU SHUTDOWN is displayed.

Question 17

In flight, if both AC transfer busses lose power,

Answer 17

the APU automatically starts, regardless of APU SEL position.

The APU can be shutdown by positioning the SEL to ON, then OFF

Question 18

Rotating the APU SEL to OFF begins the shutdown cycle by

Answer 18

closing the APU bleed air valve.

The APU continues running for a cooldown period.

The EICAS memo message APU COOLDOWN is displayed during the cooldown period.

When the cooldown period finishes, the APU shuts down.

Question 19

The APU has attended and unattended operating modes.

The attended mode operates

Answer 19

when either engine is running or starting, or when the airplane is in flight.

The unattended mode operates at all other times on the ground.

Question 20

In the attended mode, any of the following faults cause the APU to shutdown immediately

Answer 20

APU fire or

inlet over-temperature,

overspeed or

loss of overspeed protection,

an APU controller failure or

speed droop.

There is no cooldown period. The EICAS advisory message, APU SHUTDOWN, displays.

Question 21

In the attended mode For APU high EGT,

high oil temperature or

oil pressure indications,

Answer 21

the APU continues to operate and the EICAS caution message APU LIMIT is shown.

There is no cooldown period when the APU is shutdown after the APU LIMIT message is displayed.

Question 22

In the unattended mode, any of the following faults cause the APU to shutdown immediately

Answer 22

APU fire or inlet over temperature,

overspeed or loss of overspeed protection,

high EGT, low oil pressure, high oil temperature,

generator oil filter approaching bypass,

intake door failure,

APU controller failure,

speed droop,

no combustion on start,

no acceleration on start or load compressor reverse flow.

There is no cooldown period.

Question 23

When a limit is exceeded & the APU is shutdown with the selector switch:

The APU SEL is turned OFF.

Answer 23

This attempts to reset the APU controller.