Electrics

Question 1

What does the electrical system of an airplane generate and distribute?

Answer 1

AC and DC power to other airplane systems

Question 2

What are the main components of the electrical system?

Answer 2

• main AC power
• backup power
• DC power
• standby power
• flight controls power

Question 3

How does the system operation function in terms of electrical faults?

Answer 3

Electrical faults are automatically detected and isolated

Question 4

What is the primary source of electrical power in the airplane?

Answer 4

The AC electrical system

Question 5

What is the function of the Electrical Load Management System (ELMS)?

Answer 5

Provides load management and protection to ensure power availability

Question 6

What happens when electrical loads exceed available power?

Answer 6

ELMS automatically sheds AC loads by priority

Question 7

List the order of load shedding by the ELMS.

Answer 7

• galleys first
• utility busses
• individual equipment items powered by the main AC busses

Question 8

What message displays on the electrical synoptic when load shed conditions exist?

Answer 8

LOAD SHED

Question 9

What are the main AC electrical power sources?

Answer 9

• left engine integrated drive generator (IDG)
• right engine IDG
• APU generator
• primary external power
• secondary external power

Question 10

How do the main AC power sources normally operate?

Answer 10

Isolated from one another

Question 11

What occurs during power source transfers on the ground?

Answer 11

Operating sources are momentarily paralleled to prevent power interruption

Question 12

What happens when an engine starts with the GENERATOR CONTROL switch ON?

Answer 12

The IDG automatically powers the respective main bus

Question 13

How can the IDG be electrically disconnected from the busses?

Answer 13

By pushing the GENERATOR CONTROL switch to OFF

Question 14

What indicates low oil pressure in an IDG?

Answer 14

The DRIVE light illuminates and the EICAS message ELEC DRIVE FAULT L or R displays

Question 15

What is the function of the APU generator?

Answer 15

Can power either or both main busses and may be used in flight as a replacement to an IDG source

Question 16

What happens when the APU generator becomes available?

Answer 16

It automatically connects to both main AC busses if no other power source is available

Question 17

What does the PRIMARY EXT PWR switch do?

Answer 17

Connects primary external power to both main busses

Question 18

What is the purpose of the secondary external power source?

Answer 18

Can power the left and right main busses

Question 19

When is the ground service bus powered?

Answer 19

Normally powered by the right main bus

Question 20

What does the ground handling bus provide power for?

Answer 20

• cargo handling
• fueling/defueling operations
• engine turning system
• other equipment during ground operations

Question 21

What is the function of the backup electrical system?

Answer 21

Automatically provides power to selected airplane systems

Question 22

What are backup generators used for?

Answer 22

Provide backup power and supply power to the flight control DC electrical system

Question 23

What is the role of transformer-rectifier units (TRUs) in the DC electrical system?

Answer 23

Produce DC power from AC transfer busses

Question 24

What does the main battery provide?

Answer 24

Standby power to other busses

Question 25

What happens if the main battery charge is below the level required for dispatch?

Question 26

What does the hot battery bus provide power to?

Answer 26

Standby power to other busses ## Footnote See Standby Electrical System

Question 27

What maintains the main battery fully charged?

Answer 27

The main battery charger

Question 28

What message is displayed if the main battery charge is below the required level for dispatch?

Answer 28

MAIN BATTERY LOW

Question 29

How long can battery charging take with one or both engines running or with external power?

Answer 29

5-10 minutes

Question 30

What happens to battery charging time when the APU is running?

Answer 30

It goes to a slower charging mode and can take up to 18 minutes

Question 31

What does the APU battery power?

Answer 31

The APU electric starter

Question 32

What is the purpose of the TOWING POWER switch in BAT position?

Answer 32

Permits towing operations without AC power

Question 33

What does the standby electrical system provide power to?

Answer 33

Selected flight instruments, communications and navigation systems, and the flight control system

Question 34

What components make up the standby electrical system?

Answer 34

* The main battery * The standby inverter * The RAT generator and its associated generator control unit * The C1 and C2 TRUs

Question 35

What does the standby inverter do?

Answer 35

Converts DC power to AC power

Question 36

What does the RAT generator provide standby power to?

Answer 36

The C1 and C2 TRUs

Question 37

Does the RAT generator have operating time limits?

Answer 37

No

Question 38

When is the RAT deployed automatically?

Answer 38

If both AC transfer busses lose power in flight

Question 39

What systems can electrical power to some cabin and utility systems be controlled from?

Answer 39

The flight deck

Question 40

What does the IFE/PASS SEATS switch control?

Answer 40

* In-Flight Entertainment (IFE) system * Passenger seat systems * Video surveillance cameras * Flight deck personal electronic device (PED) power outlets

Question 41

What happens when the IFE/PASS SEATS Power switch is selected to OFF?

Answer 41

Power is removed from all IFE components and passenger seats

Question 42

What does the CABIN/UTILITY Power switch control?

Answer 42

Power to cabin and utility systems

Question 43

When the CABIN/UTILITY Power switch is OFF, what systems still receive power?

Answer 43

* Night lights * Reading lights * Attendant work lights * Some galley and crew rest lights

Question 44

What does the Passenger Wi-Fi switch allow?

Answer 44

On-board Wi-Fi functionality to be available to the flight crew and passengers when ON

Question 45

Fill in the blank: The standby inverter powers the AC standby bus if the _______ is not powered.

Answer 45

left transfer bus