APU

Question 1

Describe APU

Answer 1

Self-contained gas turbine

Consists of centrifugal compressor, reverse flow annular combustor and two stage axial flow turbine

Accessory gearbox drives two 225 kVA starter generators

One of the SGs changes to a starter motor for APU start

Question 2

Does the APU supply bleed air?

Answer 2

No

Question 3

What altitude limit does the APU have?

Answer 3

The APU can be started and operated up to the maximum operating altitude of the aircraft

Question 4

Moving APU switch to ON position:

Answer 4

Opens APU fuel spar valve

Activates AC or DC fuel pump

Powers the APU controller

Question 5

APU FAULT light?

Answer 5

APU fault/fire is detected

APU has shut down due to fault/fire

Momentarily during APU controller self-test

Question 6

APU status display shows:

Answer 6

Rotation speed in % RPM

EGT

Oil pressure

Oil temperature

Oil quantity in quarts

Question 7

What does the APU battery power?

Answer 7

APU controller (APUC)

Air inlet door

Right APU starter if required

Question 8

What APU items does the main battery power?

Answer 8

APU shutoff valve

DC fuel pump

Fire detection system

Question 9

How high can the APU be started without fuel pumps?

Answer 9

14,000 feet

Question 10

If starting from a cold airplane using battery power, what does the APU wait for?

Answer 10

It waits until the CCS applications are available.

The CCS fire detection and fuel management applications are necessary to start the APU

Question 11

Where is the fuel supplied for the APU come from?

Answer 11

Left fuel manifold by any operating AC pump or the DC pump in the left main tank

Question 12

When does theft aft fuel pump supply pressure for the APU?

Answer 12

Anytime AC power is supplied to the aircraft, regardless of its switch position

Question 13

How many APU starters are used for APU start?

Answer 13

One, and the starter selection is automatic unless battery power is being used, in which case only the right starter is used

Question 14

APU RUNNING memo message?

Answer 14

Displayed 2 seconds after APU reaches 95%

Question 15

APU SHUTDOWN EICAS?

Answer 15

APU failed to start, shut down automatically

Moving the APU selector to OFF from ON removes the message and resets the shutdown system, allowing another start attempt

Question 16

If you lose three generators inflight, what will happen automatically?

Answer 16

The APU will start automatically regardless of switch position

If generators are brought back, APU can be shutdown by switching ON, then OFF

If cannot get generators back, only way to shut off APU is to pull the fire switch

Question 17

APU COOLDOWN message?

Answer 17

APU in cool down mode, 2 minutes

Question 18

APU shutdown sequence

Answer 18

2 minute APU cool down

After cooldown, an APU overspeed is simulated to test the overspeed and fuel shutoff protection

This shuts off fuel and APU shuts down

APU controller closes spar valve

CCS turn off fuel pumps

At 15 RPM, APU controller shuts the inlet door

Question 19

When is the attended APU mode in effect?

Answer 19

Aircraft in flight

An engine is running or starting

Question 20

When is the APU in unattended mode?

Answer 20

On the ground when no engine is running nor starting

Question 21

In attended mode, what will cause the APU to shut down, with no cooldown period (6 items)?

Answer 21

APU Fire / Inlet temperature

Overspeed / Loss of overspeed protection

APU controller failure

Speed droop

APU start failure

Inlet door has failed closed

Question 22

APU LIMIT EICAS?

Answer 22

High EGT

High oil temperature

Low oil pressure

APU will continue to operate

No cooldown if manually shut down

Question 23

In unattended mode, ALU will shut down immediately for the following (10 items):

Answer 23

APU fire / Inlet temperature
Overspeed / Loss of overspeed protection
High EGT/Loss of EGT
Low oil pressure
High oil temperature
APU S/G oil filter approaching bypass
Air inlet door failed closed
APU controller failure
Speed droop
APU start failure