Electrical

Question 1

External Power AVAIL light

Answer 1

External power is plugged in and power quality is acceptable

Question 2

BUS Tie switch AUTO

Answer 2

• Arms automatic AC bus tie circuits
• Arms automatic DC bus tie circuits
• Arms automatic flight instrument transfer bus circuits

Question 3

Generator DRIVE light illuminated or L/R GEN DRIVE EICAS

Answer 3

• Generator drive oil temperature is high

* Generator drive oil pressure is low

Question 4

Battery Switch ON

Answer 4

Unpowered aircraft on the ground:
- allows starting of the APU

Inflight or on the ground after AC power removed:
- standby and battery busses are powered

Question 5

Main aircraft AC Power Sources

Answer 5

• Left and Right Integrated Drive Generators (IDGs)
• APU generator
• two sources required to supply entire aircraft AC load
• external power can also supply entire aircraft

Question 6

How is AC power distributed

Answer 6

• Left Main AC bus
• Right Main AC bus
• ground service bus

Question 7

Source priority for powering L and R main AC busses

Answer 7

• Respective IDG
• APU generator
• Opposite IDG

*EXT power has highest priority if available and selected

Question 8

Power source of Ground Service Bus

Answer 8

Primary:
Right Main AC BUS

Alternate:

• APU Gen
• EXT power

Question 9

What is powered by ground service bus?

Answer 9

• Main battery charger
• APU battery charger
• Aft No.1 E/E cooling fan
• Left forward fuel pump
• Main deck cargo lighting

Question 10

What powers Ground Handling Bus?

Answer 10

• can only be powered on the ground

- APU or EXT pwr only

Question 11

What is powered by the Ground Handling Bus?

Answer 11

• Lower cargo compartment lights
• Equipment necessary for cargo handling
• Aircraft refueling features

Question 12

Power source of CA and FO Flight Instrument Transfer busses

Answer 12

CA flight instrument transfer bus:
Primary - Left main AC Bus
Alternate - Right main AC Bus

FO flight instrument transfer bus:
Primary - Right main AC Bus
Alternate - Left main AC Bus

• If a Bus Tie switch is manually opened, flight instrument switching will not occur*

Question 13

Electrical Configuration during AUTOLAND

Answer 13

• during 3 autopilot approach busses isolate to allow three independent power sources
• Left main system powers the left autopilot and the Captain’s flight instrument transfer bus
• Right main system powers the right autopilot and the First Officer’s flight instrument transfer bus
• Battery/standby system powers the center autopilot

Question 14

When does electrical load shedding occur?

Answer 14

• if electrical loads exceeds owner available electrical load shedding automatically occurs
• utility busses shed first followed by individual items on the main AC busses
• power restored in reverse order

Question 15

Engine Start Load shedding

Answer 15

• when APU is used for both electrical and pneumatic power during engine start
• First engine start selector moved to GND —> both utility busses trip
• Second engine start selector moved to GND —> respective utility bus trips

Question 16

Generator Loss Load Shedding

Answer 16

• Loss of an IDG causes both utility busses to trip

- engine shutdown inflight will shed respected center tank fuel boost pump

Question 17

Component of DC electrical system

Answer 17

• 2 TRUs (L and R powered by respective Main AC bus)
• Left Main DC Bus
• Right Main DC Bus
• Standby DC Bus (primary power source: Left DC Bus; alternate power source: main battery)
• Battery Bus (primary power source: Left DC Bus; alternate power source: main battery)
• Main Battery

Question 18

Components of standby/battery system

Answer 18

• Hot Battery Bus
• Battery Bus
• AC standby bus
• DC standby bus

Question 19

Power source of Hot Battery Bus

Answer 19

• Prior to electrical power —> Main Battery

- After electrical power —> main battery charger

Question 20

Components powered by Hot Battery Bus

Answer 20

• clock’s time reference
• fire extinguisher bottles
• APU fuel valve
• spar fuel valve
• parking break valve
• IRS emergency power (R continuously, L and C for 5 mins)
• landing gear alternate extension
• RAT Manual deployment

Question 21

Power source of AC Standby Bus

Answer 21

With STBY power selector in AUTO:

• Prior to electrical power —> main battery via STBY inverter
• After electrical power —> Left AC Power system

Question 22

Components on Battery Bus

Answer 22

• APU fuel valve
• DC fuel pump
• Engine anti-ice
• Engine, APU and cargo fire detection
• Engine driven hydraulic pump shutoff valves
• Engine fuel control valves
• Engine start controls
• Fuel crossfeed valves
• Generator Control
• Hydraulic PTU control

Question 23

Components on DC STBY bus

Answer 23

Left aural warning speaker
Left stick shaker
Left VHF comm system
Left yaw damper
Manual cabin altitude pressure control
Rudder ratio changer
Rudder trim
Stab trim shutoff valves
Standby Attitude Indicator

Question 24

Components on AC STBY Bus

Answer 24

Cabin altitude/differential pressure indications
Center ILS system
Engine ignition
Left navigation system (VOR, Air Data Computer (ADC) RDMI)
Left yaw damper
Main panel flood lights
Standby Instrument Panel lights
Three spoiler pairs
Wheel well fire detection

Question 25

AC Transfer Busses (767)

Answer 25

- power items considered necessary for ETOPS - Primary power source —> respective Main AC bus - Alternate power source —>Hydraulic Driven Generator

Question 26

Hydraulic Driven Generator (767)

Answer 26

- backup source of power in the event that both main AC busses become inoperative - powered by center hydraulic system Provides AC power for: • Left AC transfer bus • Right AC transfer bus • Standby AC bus (through the left AC transfer bus) • Captain's flight instrument transfer bus Provides DC power for: • Hot battery bus • Battery bus • Standby DC bus

Question 27

How many EICAS computers?

Answer 27

- 2 x EICAS computers (L and R) - Left Primary, Right backup - with selector in AUTO R will automatically takeover if L fails

Question 28

What is powered by the Hyd Driven Generator (HDG) - 767

Answer 28

``` ♦ Battery bus – and – ♦ Hot battery bus – and – ♦ Standby AC bus – and – ♦ Standby DC bus – and – ♦ Left transfer bus – and – ♦ Right transfer bus – and – ♦ Captain flight instruments transfer bus ```

Question 29

Amber ISLN light illuminated (L or R BUS ISOLATED advisory)

Answer 29

− Bus Tie switch is off – or – − Fault has occurred – and – − AC bus tie breaker open

Question 30

How long can the main batteries supply STBY power

Answer 30

30 mins

Question 31

What does the Ground Service bus power when powered from ground handling bus?

Answer 31

♦ Main deck cargo lights – and – ♦ Left forward fuel pump (for APU) – and – ♦ Battery chargers (main and APU) – and – ♦ Aft No. 1 E/E fan

Question 32

What causes Utility Busses load shedding?

Answer 32

• (B767) Utility busses load shed for: o - Generator loss – or – o - Overloaded engine generator • (B757) Utility busses load shed for: o - Engine start (Both for 1st Eng Start, Respective for 2nd Eng Start) – or – o - Generator loss – or – o - Overloaded engine generator

Question 33

Automatic Electric Load Shedding

Answer 33

Power removed from: − Respective Center Fuel pump if N2 < 50% (RR N3 < 50%) − Center #2 Hydraulic Electric Primary pump during first engine start − Left Hydraulic Electric Demand pump (during both engine starts) − (B757) Utility busses: ♦ Both shed during first engine start ♦ Respective sheds during second engine start

Question 34

Power source for 3 APs during autoland (after isolation)

Answer 34

Left main AC/DC powers left autopilot and CAPT flight instruments − Right main AC/DC powers right autopilot and F/O flight instruments − Battery/Standby system powers center autopilot

Question 35

What IRS’s are powered after a loss of all AC power

Answer 35

767: - left and right continuously - right shuts down after 5 mins 757: - right continuously - left and center shut down after 5 mins