Electrical CBT's

Question 1

What does the single synchronous bus do?

Answer 1

It keeps all electrical busses powered even when IDG’s or other sources may be down. (tie bus).

Question 2

How many APU’s? GPU’s?

Answer 2

1 APU (2 APU generators)

2 GPU’s

Question 3

How many TRU’s?

Answer 3

4

Question 4

Each IDG normally powers____

Answer 4

its relative AC bus

Question 5

Can APU electrical be used in flight?

Answer 5

No

Question 6

Can you reconnect an IDG after disconnecting it?

Answer 6

No, only MX can on the ground.

Question 7

Can 1 IDG (or 1 APU/GPU) source be enough to power the entire electrical system?

Answer 7

Yes

Question 8

Does the 747 have no-break power source meshing by matching voltage and frequency momentarily before switching?

Answer 8

Yes

Question 9

What is a GCB?

Answer 9

Generator Control Breaker. (OFF for IDG. Just above the IDG disconnect button.)

Question 10

What causes the EICAS message: ELECTRIC DRIVE (1) (2) (3) or (4)

Answer 10

-High Oil Temp
-Low Oil Pressure
-Uncorrectable Frequency Fault

Question 11

What condition automatically disconnects an IDG?

Answer 11

High IDG Oil Temperature

Question 12

What items are on the main deck cargo handling bus?

Answer 12

-Main Deck Cargo Handling Equipment and lights

-Nose and Side Cargo Doors

Question 13

What items are on the ground service bus?

Answer 13

· battery chargers

· Fuel pumps for APU start

· Flight deck flood and service lights

Nav lights

· Miscellaneous service outlets and
equipment

Question 14

What powers the Captain transfer bus? FO transfer bus? What is the backup?

Answer 14

CA: AC Bus 3

FO: AC Bus 2

Common backup: AC Bus 1

Question 15

What is an ELCU?

Answer 15

Electrical Load Control Unit.

They are on each utility bus and protect the system against utility faults by load shedding.

Question 16

What do utility busses power?

Answer 16

· Forward main fuel pumps 2 and 3

· Forward override/jettison pumps
2 and 3

· Center override/jettison pump

· Galley Equipment

Question 17

What is a DCIR? What do they do?

Answer 17

DC Isolation Relay. They allow the DC busses to be connected to the main DC tie bus, so they can stay powered if that particular TRU is down or fails.

Question 18

What will happen if there is a fault in an AC bus and the bus ties are in AUTO?

-What about if you press the bus tie to OFF (ISLN)?

Answer 18

The logic is to isolate that one AC bus only, keeping the DC DCIR online to continue power to that associated DC bus.

-If you turn the bus tie to OFF (ISLN), it not only isolates that associated AC bus, but it will also open the DCIR and that associated DC bus will not be powered. (this is why normal operation is to leave it in AUTO, because there is no way to manually disconnect the DC bus, its paired always with AC.)

Question 19

The main and APU battery busses are normally powered by ______.

Answer 19

DC Bus 3 (Normally)

DC Bus 3 offline: each buss’s associated hot battery bus.

Question 20

If either AC bus 3 or DC bus 3 is unpowered, what powers the APU or main battery busses?

Answer 20

Each battery bus would be powered by its related hot battery bus

Question 21

Name the 2 batteries on the DC system

Answer 21

• Main battery
• APU Battery

Question 22

How many battery chargers are there? What are they called?

Answer 22

2. They are the main battery charger and the APU battery charger.

Question 23

What do the battery chargers do? What are they powered by?

Answer 23

They act as TRU’s to supply power to the associated battery bus (either main or APU) and also keep the batteries fully charged.

Normally powered by the ground service bus.

Question 24

During an autoland approach, AC and DC busses _______ are isolated from the synchronous bus to provide independent power sources for the three autopilots. AC bus _____continues to power the synchronous bus.

Answer 24

1, 2, and 3

4

Question 25

What synoptic page is inhibited during autoland?

Answer 25

Electrical

Question 26

Autoland electrical isolation is cancelled when any of the following conditions happen:

Answer 26

• All autopilots disengage

• TO/GA mode is annunciated and the airplane is higher than 100 feet radio altitude

• Approach mode is disarmed or deselected

• Electrical system unable to maintain a configuration for autoland bus isolation.

Question 27

What normally powers the main standby bus?

Answer 27

AC bus 3

Question 28

If AC bus 3 not powered, the main standby bus is powered by the _________.

Answer 28

main standby inverter.

(The main standby inverter, normally unpowered, is activated and receives power from the main battery bus through the hot battery bus. The main battery can provide power to the main standby bus for a minimum of 30 minutes.)

Question 29

The APU standby bus is normally powered by

Answer 29

The captain transfer bus