6 - Electrical

Question 1

What does the APU Generator (APU GEN) Control Switch do?

Answer 1

• arms APU generator breaker to automatically close
• opens APU generator breaker
• resets fault trip circuitry

Question 2

What do the BUS TIE Switches do?

Answer 2

• arms/opens automatic AC bus tie circuits
• arms/opens automatic DC bus tie circuits
• arms/opens automatic flight instrument transfer bus circuits
• resets fault trip circuitry

(Flight instrument transfer bus auto transfer for BUS OFF only if BUS TIE switch is in AUTO)

(Both BUS TIE breakers must be in AUTO for DC bus tie breaker to work)

Question 3

What do the Generator Control (GEN CONT) Switches do?

Answer 3

• arms the generator breaker to close automatically when generator power is available
• opens generator breaker
• resets fault trip circuitry

Question 4

External Power Available (AVAIL) Light

Illuminated (white) –

Answer 4

external power is plugged in and power quality is acceptable

Question 5

What do the UTILITY BUS Switches do?

Answer 5

• connects/disconnects utility and galley busses to main AC bus
• resets overload/load shed circuitry

Question 6

What happens when you push a GEN DRIVE DISC Switch?

Answer 6

• disconnects generator drive from the engine

* requires maintenance action on the ground to reconnect the generator drive.

Question 7

What does a Generator DRIVE light indicate?

Answer 7

• the generator drive oil temperature is high

* the generator drive oil pressure is low

Question 8

What happens with the BAT switch ON:

• Unpowered airplane
• Powered airplane (when AC power is lost/removed)

Answer 8

• a few annunciator lights illuminate
• allows the APU to be started

• the standby and battery busses are powered (with STBY POWER in AUTO)

Question 9

What happens if AC power is lost with Standby (STBY) POWER Selector in AUTO?

How long will it last?

Answer 9

the standby busses transfer to battery power (Main and APU)

90 min

Question 10

A hydraulic driven generator operates _____ as a backup source of power in the event _____

Answer 10

automatically (no time limit)

both main AC busses lose power

(less than 1/10 the power of an engine driven generator)

(may have BAT DISCH light because HDG DC output low)

Question 11

The source order for powering left/right main busses is:

Answer 11

• respective IDG
• APU generator
• opposite IDG

Question 12

The ground service bus is normally powered by _____

Alternate sources of power for the ground service bus are _____

Answer 12

right main bus

• the APU generator
• external power

Question 13

The ground service bus powers:

Answer 13

• the main battery charger
• the APU battery charger
• miscellaneous cabin and system loads

Question 14

The ground handling bus is powered (only on the ground) by _____ , and powers ______

Answer 14

APU generator or external power source

cargo handling and equipment

Question 15

During autoland, the busses isolate to allow three independent sources to power the three autopilots:
• the left main system powers _____
• the right main system powers _____
• _____ powers the center autopilot

Answer 15

• the left autopilot and the captain’s flight instrument transfer bus
• the right autopilot and the first officer’s flight instrument transfer bus
• the battery/standby system

(Reverts to normal for autopilot GA or disengage)

Question 16

Normally, the captain’s flight instruments are powered by _____ and the first officer’s flight instruments are powered by _____

If the bus tie breakers are in AUTO, the flight instrument transfer busses transfer to _____

If power is lost to both main AC busses, the captain’s flight instruments are powered by _____

Answer 16

left main AC Bus

right main AC Bus

opposite main AC bus

hydraulic driven generator.

Question 17

Left and right AC transfer busses power items considered necessary for ETOPS (which are not powered by the battery/standby system)

Transfer busses are normally powered by _____ ,
but also can be powered by _____ when both AC busses are unpowered

Answer 17

associated main AC busses

Hydraulic Driven Generator

Question 18

The main DC electrical system uses _____ to produce DC power, which are powered by _____

Answer 18

transformer-rectifier units (TRUs)

main AC busses

Question 19

The TRUs operate isolated from one another

If one TRU fails, the ______ closes to keep both DC busses powered

Both _____ switches must be in AUTO for the _____ to close

Answer 19

DC bus tie breaker

BUS TIE

DC bus tie breaker

Question 20

Where are the flight deck controls for the main DC electrical system located?

Answer 20

There are no flight deck controls for the main DC electrical system

Question 21

The Battery/Standby Power System consists of the following busses:

Answer 21

• the hot battery bus
• the battery bus
• the standby AC bus
• the standby DC bus

Question 22

What is the power source for the hot battery bus?

Answer 22

• Main battery

- Battery charger powered from the ground service bus

Question 23

Prior to establishing electrical power _____ powers the hot battery bus

After establishing electrical power _____ powers the hot battery bus

Answer 23

main battery

main battery charger (powered by the Ground Service Bus)

Question 24

After establishing electrical power _____ powers the battery bus, and _____ provides a backup source of power

Answer 24

left DC system

main battery

Question 25

What does the HDG (Hydraulic Driven Generator) power? (7, 4-AC, 3-DC)

Answer 25

- CA Flight Instrument Transfer bus - L AC Transfer bus - R AC Transfer bus - Stby AC bus - Stby DC bus - Battery bus - Hot Battery bus (L FMC, flap posit, auto press controllers, stby engine indications, ISFD, CA pitot heat)

Question 26

What happens if you get an APU FAULT light?

Answer 26

immediate automatic shutdown (no cool down)

Question 27

How long can the Main Battery power the STBY Power system?

Answer 27

30 min | CBT says 90 min for Main and APU batteries

Question 28

On STBY Power if battery is depleted (30 min), what is the effect on flaps and gear?

Answer 28

C ADP pneumatic supply valve closes with loss of DC power. No way to hydraulically operate flaps and gear.

Question 29

What happens when you place BAT switch to ON?

Answer 29

allows battery to power Battery Bus if no other source is available

Question 30

What happens with STBY POWER selector to AUTO?

Answer 30

the STBY busses transfer to battery power if normal AC power is lost (AC STBY bus normally powered by L AC bus. If L AC power is lost, DC tie bus powers STBY Inverter. If both AC busses are unpowered, main BAT powers STBY Inverter) (DC STBY bus normally powered by L DC bus)

Question 31

What does a STBY POWER OFF light mean?

Answer 31

loss of power to STBY AC and/or STBY DC bus

Question 32

What does a Bus Tie ISLN light mean? Due to _____ (2)

Answer 32

BTB open due to a fault or switch OFF

Question 33

What does a GEN Drive Disc DRIVE light mean?

Answer 33

high oil temp or low oil press

Question 34

What does a Gen Cont OFF light mean?

Answer 34

generator breaker open

Question 35

When do utility busses shed? (4) | The galley bus is powered by the left utility bus, and has no direct controls or indications

Answer 35

BOSS B - both T/Ls TO range on ground with engines shutdown O - overload of available electrical power S - starting engines S - single GEN source

Question 36

What is max altitude for APU power?

Answer 36

FL 431

Question 37

What happens to the APU if you get an APU FAULT light?

Answer 37

immediate automatic shutdown with no cool down

Question 38

APU Starter limit

Answer 38

3 attempts in 60 min

Question 39

What happens if BAT Switch is turned OFF with APU running?

Answer 39

APU shutdown after cool down cycle without fire detection

Question 40

Hot Battery Bus powers (10) | regardless of BAT switch position

Answer 40

- Clock time base - IRS emergency power - Equipment cooling ground warning - Fire extinguisher bottles - Fueling system - APU fuel shutoff valve - Wing spar fuel shutoff valve - Alternate landing gear extension - Parking brake valve - RAT manual deployment

Question 41

What is powered from the Battery Bus? (5)

Answer 41

- Fire detection - PA system - Fuel quantity indicating system - Stby engine indications - Alternate stab trim

Question 42

What is powered by the STBY POWER system? (5)

Answer 42

- Stby instruments - L VHF, VOR, RDMI - C ILS - Instrument panel flood lights - Manual pressurization control

Question 43

Normal load shedding during engine start (3)

Answer 43

- an electric hydraulic pump - center tank fuel pumps - utility buses

Question 44

How is the Ground Handling Bus powered and what is on the bus?

Answer 44

EXT (AVAIL) or APU - Cargo systems - Cargo lights - Maint access lights - Fueling systems

Question 45

How is the Ground Service Bus powered and what is on the bus?

Answer 45

- R main bus - APU - EXT - Main/APU battery chargers - Left forward fuel pump - Cabin lighting and outlets - Misc cabin and system loads

Question 46

What happens with a L or R BUS OFF light illuminates? | only if BUS TIE switches in AUTO

Answer 46

- Flight instrumental transfer bus switches to other bus - DC bus tie closes to keep the DC busses powered - (L bus fail) Stby AC bus powered from the Stby Inverter - (R bus fail) Lower EICAS screen blanks

Question 47

If EXT power is powering both main busses what happens when the APU is started and APU GEN becomes available? What happens if IDGs or APU Gen are powering both main busses and EXT is selected ON?

Answer 47

Nothing. EXT continues to power both busses until switched off. EXT powers both main busses