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