Electrical System

Question 1

What are the Main AC power sources on the 747-400, 747-8, and LCF?

Answer 1

4 x IDG’s
2 x External Power Sources
2 x APU Generators (747-400 & 747-8 Only).

Question 2

What is the function of the Standby Power Switch in the AUTO position?

Answer 2

To allow the Main and APU Standby Busses to be powered from available sources.

Question 3

What does the ‘AVAIL’ light indicate on the EXT and APU PWR switches?

Answer 3

The related power sources is armed and available, and the power quality is acceptable.

Question 4

When is the Main Cargo Deck Handling bus powered?

Answer 4

When the ‘AVAIL’ light for either EXT 2 or APU 2 is illuminated (available, but not currently in use).

Question 5

What electrical power source provides power for the Lower Lobe Cargo Handling, Fueling Panel, and AUX 4 Hydraulic Pump?

Answer 5

Ground Handling Bus, powered by either EXT PWR 1 or APU GEN 1.

Question 6

What are some items powered by the Utility Busses?

Answer 6

5 Fuel Pumps,
Galley Equipment

Question 7

What happens when you push a Generator Drive Disconnect (DRIVE DISC) switch? (2 Items)

Answer 7

The associated IDG is disconnected from the engine, and
The associated GCB opens.

Question 8

What condition automatically disconnects the IDG?

Answer 8

Excessive Drive Oil Temperature

Question 9

What does a Bus Isolation (ISLN) light indicate? (2 Items)

Answer 9

BTB Open, and
AC bus is isolated from the Synchronous Bus

Question 10

How do you reconnect an IDG that has been disconnected?

Answer 10

Maintenance Only. Cannot be reconnected by flight crew in flight.

Question 11

How is the electrical system configured during an Autoland? (2 Items)

Answer 11

AC & DC Busses 1, 2, and 3 are isolated from the Synchronous Bus, and
AC Bus 4 continues to power the Synchronous Bus.