Main Electrical Components

Question 1

In normal inflight ops, all electrical power is provided by?

Answer 1

2 engine driven generators

Question 2

There’s a 3rd generator available in flight. What is it driven by?

Answer 2

APU. (It’s equal in size & capacity to either engine driven generator)

Question 3

How many generators are required in flight to meet all electrical demands?

Answer 3

Any 2 of the 3

Question 4

What happens if only 1 generator is available in flight?

Answer 4

An electrical load management system automatically shuts down some low priority items (e.g galleys)

Question 5

What distributes power to all airplane electrical systems?

Answer 5

2 main AC power busses (L&R)

Question 6

What ensures both main busses remain powered at all times?

Answer 6

A bus tie & 2 isolation relays

Question 7

Where are the controls for the electrical system located?

Answer 7

On the overhead panel (above the captain)

Question 8

With all electrical power switched off, the main battery still continues to power a few important items through?……

Answer 8

The Hot Battery Bus

Question 9

What important items does the Main Battery continue to power, through the Hot Battery Bus, even with all electrical power switched off?

Answer 9

1. Engine fire extinguisher bottles
2. APU fire extinguisher bottle
3. ADURU - as long as the ADIRU switch is on

Question 10

How many external power switches are there?

Answer 10

2 - primary & secondary

Question 11

What does the ‘AVAIL’ light on the external power switch indicate?

Answer 11

External power is connected to the airplane & is of usable quality.

Question 12

With a single external power source, on the ground, will every electrical item be powered?

Answer 12

No, some non-essential electrical items e.g galleys May be unpowered if loads are high

Question 13

Connecting secondary external power to the airplane gives ……….. electrical load capacity for most ground situations

Answer 13

Full

Question 14

When both primary & secondary external power are available primary power powers the ………. Bus & secondary power powers the ……… Bus

Answer 14

Primary powers the right main bus

Secondary powers the left main bus

Question 15

How many power sources support full electrical load?

Answer 15

Any 2

Question 16

When the APU is running & primary external power is online, the APU powers the …….. main bus & the primary external source powers the …….. main bus

Answer 16

APU - Left Main Bus

Primary External power - Right Main Bus

Question 17

What position is the APU GEN switch normally left in?

Answer 17

ON.

The APU GEN breaker opens & closes automatically.

Question 18

There’s no interruption of power when switching power sources except when ?

Answer 18

Switching between 2 external sources.

Question 19

Each main generator & its drive unit are housed in a single case & share a common oil supply. What is this unit called?

Answer 19

An Integrated Drive Generator (IDG)

Question 20

What controls the IDG & what does it provide?

Answer 20

Controlled by a generator control unit.

Provides automatic control functions & system protection.

Question 21

The generator control switches automatically connect the IDG to ?

Answer 21

The Main Busses (L &R)

Question 22

What does the ‘OFF’ light mean on the APU GEN switch?

Answer 22

Means Fault or switch is off

Question 23

What does the ‘OFF’ light mean on the GEN CTRL switch mean?

Answer 23

Means “Breaker Open”

Question 24

What happens to the electrical system when you start the #2 engine?

Answer 24

1. IDG rotates to operating speed
2. The generator breaker closes
3. The right Gen now powers the right main bus
4. Simultaneously, Primary & Secondary ext power auto disconnect from Main busses, the Right Gen also powers the Left Main Bus
5. After a few seconds with the APU running, APU power replaced Right Gen power on the Left main bus.

Question 25

Each main AC bus powers how many utility busses?

Answer 25

1 utility bus

Question 26

The bus tie breakers are normally left in AUTO, why?

Answer 26

The bus tie breakers keep both main busses powered at all times from any available source in a priority order

Question 27

Bus Tie Breakers keep busses powered in what priority order?

Answer 27

1. Associated engine generator
2. APU Generator
3. Opposite engine generator

Question 28

External power is the only AC power source which is ?

Answer 28

Not automatically selected.

You must apply it manually.

Question 29

What position are the bus tie breakers in whenever the IDGs are powering their respective busses?

Answer 29

Open

Question 30

If the L BUS TIE switch is selected to ‘ISLN’ can the R BUS TIE close? What effect does this have if both engines are running & both engine generators are powering their associated bus?

Answer 30

No.

None.

Question 31

One generator can power…….

Answer 31

All essential flight loads

Question 32

If there’s only 1 power source available, the ELMS does what?

Answer 32

The Electrical Load Management System load sheds non-essential loads.
1st - Galleys & galley chillers
2nd - L & R utility busses

Question 33

The Main Battery powers ?

Answer 33

1. The standby power system
2. Captains displays & CDU
3. The left AIMS (Airplane Information Management System)

Question 34

You have an unpowered airplane. Which items will be powered if you push the BATTERY switch to ON?

Answer 34

The Battery Bus

Question 35

Power is removed from which items when the battery switch is pushed OFF during power down?

Answer 35

Power is removed from the standby bus, Captain’s flight instruments, & left AIMS.