Electrical Flashcards
External Power AVAIL light
External power is plugged in and power quality is acceptable
BUS Tie switch AUTO
- Arms automatic AC bus tie circuits
- Arms automatic DC bus tie circuits
- Arms automatic flight instrument transfer bus circuits
Generator DRIVE light illuminated or L/R GEN DRIVE EICAS
- Generator drive oil temperature is high
* Generator drive oil pressure is low
Battery Switch ON
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
Main aircraft AC Power Sources
- 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
How is AC power distributed
- Left Main AC bus
- Right Main AC bus
- ground service bus
Source priority for powering L and R main AC busses
- Respective IDG
- APU generator
- Opposite IDG
*EXT power has highest priority if available and selected
Power source of Ground Service Bus
Primary:
Right Main AC BUS
Alternate:
- APU Gen
- EXT power
What is powered by ground service bus?
- Main battery charger
- APU battery charger
- Aft No.1 E/E cooling fan
- Left forward fuel pump
- Main deck cargo lighting
What powers Ground Handling Bus?
- can only be powered on the ground
- APU or EXT pwr only
What is powered by the Ground Handling Bus?
- Lower cargo compartment lights
- Equipment necessary for cargo handling
- Aircraft refueling features
Power source of CA and FO Flight Instrument Transfer busses
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*
Electrical Configuration during AUTOLAND
- 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
When does electrical load shedding occur?
- 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
Engine Start Load shedding
- 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
Generator Loss Load Shedding
- Loss of an IDG causes both utility busses to trip
- engine shutdown inflight will shed respected center tank fuel boost pump
Component of DC electrical system
- 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
Components of standby/battery system
- Hot Battery Bus
- Battery Bus
- AC standby bus
- DC standby bus
Power source of Hot Battery Bus
- Prior to electrical power —> Main Battery
- After electrical power —> main battery charger
Components powered by Hot Battery Bus
- 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
Power source of AC Standby Bus
With STBY power selector in AUTO:
- Prior to electrical power —> main battery via STBY inverter
- After electrical power —> Left AC Power system
Components on Battery Bus
- 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
Components on DC STBY bus
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
Components on AC STBY Bus
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
AC Transfer Busses (767)
- power items considered necessary for ETOPS
- Primary power source —> respective Main AC bus
- Alternate power source —>Hydraulic Driven Generator
Hydraulic Driven Generator (767)
- 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
How many EICAS computers?
- 2 x EICAS computers (L and R)
- Left Primary, Right backup
- with selector in AUTO R will automatically takeover if L fails
What is powered by the Hyd Driven Generator (HDG) - 767
♦ 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
Amber ISLN light illuminated (L or R BUS ISOLATED advisory)
− Bus Tie switch is off – or –
− Fault has occurred – and –
− AC bus tie breaker open
How long can the main batteries supply STBY power
30 mins
What does the Ground Service bus power when powered from ground handling bus?
♦ Main deck cargo lights – and –
♦ Left forward fuel pump (for APU) – and –
♦ Battery chargers (main and APU) – and –
♦ Aft No. 1 E/E fan
What causes Utility Busses load shedding?
• (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
Automatic Electric Load Shedding
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
Power source for 3 APs during autoland (after isolation)
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
What IRS’s are powered after a loss of all AC power
767:
- left and right continuously
- right shuts down after 5 mins
757:
- right continuously
- left and center shut down after 5 mins
