Chapter 6 - Electrical

Question 1

What do the APU GEN and GEN CONT switches do ?

Answer 1

They ARM to close the breaker when power is available.

Question 2

When do the APU GEN and GEN CONT OFF light illuminate ?

Answer 2

Whenever the breaker is open (because power is not available).

Question 3

What does the BUS TIE switch do ?

Answer 3

It arms:

• The AC bus tie
• The DC bus tie
• The respective flight instrument transfer bus

Question 4

When does the bus tie ISLN light illuminate ?

Answer 4

When the AC bus tie breaker is open.

Not in case of the DC bus tie.

Question 5

How can the load shed circuitry be reset ?

Answer 5

By recycling the UTILITY BUS switch.

Question 6

When does the generator DRIVE light illuminate ?

Answer 6

When the oil pressure is low OR oil temperature is high.

Question 7

Can a generator disconnect be reset in-flight ?

Answer 7

No.

Question 8

When does the standby power OFF light illuminates ?

Answer 8

When the AC or DC standby bus or the battery bus is not powered.

Question 9

When does the battery OFF light illuminate ?

Answer 9

When the battery switch is off.

Question 10

Can one AC source power the whole electrical load ?

Answer 10

No. Two sources are required for the full load.

Question 11

If APU is running and external power is connected, is the APU powering the main busses ?

Answer 11

No.

Question 12

What is priority of AC power sources ?

Answer 12

• Ground power
• IDG
• APU
• Opposite IDG

Question 13

Are there any indications or EICAS messages for a galley bus which is not powered.

Answer 13

No. Only when the utility bus is not powered as well.

Question 14

Which bus powers the GND SVC bus ?

Answer 14

R MAIN AC BUS.

Question 15

How is the GND HANDLING bus powered ?

Answer 15

From the APU GEN or from external power.

Question 16

What happens above 200 ft in case of loss of a generator during an autoland ?

Answer 16

> 200ft, the bus ties close again. The L main AC system powers the center autopilot. NO LAND 3 is shown.

Question 17

During autoland, how is the center autopilot powered ?

Answer 17

By the standby power system.

Question 18

What happens with the AC bus ties during autoland ?

Answer 18

They open.

Question 19

How are the flight instruments powered in case of loss of both generators ?

Answer 19

By the HDG.

Question 20

Are the transfer busses powered in case of loss of both generators ?

Answer 20

Yes, by the HDG.

Question 21

What is the order of AC load shedding ?

Answer 21

• Galley bus
• Utility bus
• Main AC items

Question 22

Is load shedding automatically reverted ?

Answer 22

Yes.

Question 23

Before engine start, two load sheddings may occur:

Answer 23

• one electric hydraulic pump

- center tank fuel pumps

Question 24

During engine start, one load shedding may occur:

Answer 24

Utility busses

Question 25

What happens on the ground, when the engines are shut down, and the thrust levers are advanced ?

Answer 25

It may cause inadvertent load shedding of the utility busses. Solution: return the thrust levers to idle, and recyle the UTILITY BUS switches.

Question 26

Is the DC bus tie armed when only one BUS TIE switch is in auto ?

Answer 26

No.

Question 27

The standby power system consists of:

Answer 27

battery bus hot battery bus AC standby bus DC standby bus

Question 28

How is the battery bus powered ?

Answer 28

By the L DC bus or the main battery.

Question 29

How is the DC standby bus powered ?

Answer 29

By the L DC bus or by a combination of: | - the main battery AND APU battery.

Question 30

How is the AC standby bus powered ?

Answer 30

By the L AC TRANSFER BUS or by a combination of: | - the main battery AND APU battery + inverter

Question 31

When is the HDG activated ?

Answer 31

When the L AND the R MAIN AC bus are not powered.

Question 32

Is the amount of power of the HDG more than that of full batteries ? What is the consequence ?

Answer 32

No. Consequence is that initially BAT DISCH for both batteries may occur.

Question 33

What busses are lost in case of a failure of L AC main bus ?

Answer 33

L AC transfer bus L utility bus L galley bus